diff --git a/src/main/kotlin/exercise6/task1/SimpleGenerics.kt b/src/main/kotlin/exercise6/task1/SimpleGenerics.kt
index edf9790..ebd905b 100644
--- a/src/main/kotlin/exercise6/task1/SimpleGenerics.kt
+++ b/src/main/kotlin/exercise6/task1/SimpleGenerics.kt
@@ -14,9 +14,9 @@ package exercise6.task1
 /**
  * A binary tree node that holds some value.
  */
-private data class TreeNode(val value: Any) {
-    var left: TreeNode? = null
-    var right: TreeNode? = null
+private data class TreeNode<T>(val value: T) {
+    var left: TreeNode<T>? = null
+    var right: TreeNode<T>? = null
 }
 
 /**
@@ -42,8 +42,7 @@ private fun printNodes(): String {
 
     val decisionI = Decision("Do you choose a red or a blue pill?", "Red", "Blue")
     val decisionTree = TreeNode(decisionI)
-    TODO("Uncomment code bellow and make the file compilable")
-//    return "${genealogyTree.value.name} ${decisionTree.value.answerLeft}"
+    return "${genealogyTree.value.name} ${decisionTree.value.answerLeft}"
 }
 
 fun main() {
diff --git a/src/main/kotlin/exercise6/task2/UpperBoundConstraints.kt b/src/main/kotlin/exercise6/task2/UpperBoundConstraints.kt
index 53e84c0..788dd5d 100644
--- a/src/main/kotlin/exercise6/task2/UpperBoundConstraints.kt
+++ b/src/main/kotlin/exercise6/task2/UpperBoundConstraints.kt
@@ -38,9 +38,8 @@ private data class SetIntersection(val size: Int): CostElement {
  * nodes. This code is not yet compilable, but it will become compilable as soon as you add an upper bound to the generic
  * type.
  */
-private fun <T> calculateTreeCost(root: TreeNode<T>): Double {
-    TODO("Uncomment code bellow and make the file compilable")
-//    return root.value.cost +
-//            (root.left?.let { calculateTreeCost(it) } ?: 0.0) +
-//            (root.right?.let { calculateTreeCost(it) } ?: 0.0)
+private fun <T : CostElement> calculateTreeCost(root: TreeNode<T>): Double {
+    return root.value.cost +
+            (root.left?.let { calculateTreeCost(it) } ?: 0.0) +
+            (root.right?.let { calculateTreeCost(it) } ?: 0.0)
 }
\ No newline at end of file
diff --git a/src/main/kotlin/exercise6/task3/UpperBoundConstraintPartTwo.kt b/src/main/kotlin/exercise6/task3/UpperBoundConstraintPartTwo.kt
index 72a660a..edd5032 100644
--- a/src/main/kotlin/exercise6/task3/UpperBoundConstraintPartTwo.kt
+++ b/src/main/kotlin/exercise6/task3/UpperBoundConstraintPartTwo.kt
@@ -49,7 +49,7 @@ private data class SetIntersection<S>(val size: Int, val lowerBound: S?, val upp
  * no intersection at all. If the intersection is likely to be not empty, it estimates the intersection size as the mean
  * of the set sizes.
  */
-private fun <T> estimateIntersectionSize(treeNode: TreeNode<SetIntersection<T>>): Int {
+private fun <T : Comparable<T>> estimateIntersectionSize(treeNode: TreeNode<SetIntersection<T>>): Int {
     val leftNode = treeNode.left ?: return treeNode.value.size
     val rightNode = treeNode.right ?: return treeNode.value.size
 
@@ -60,9 +60,8 @@ private fun <T> estimateIntersectionSize(treeNode: TreeNode<SetIntersection<T>>)
         return 0
     }
 
-    TODO("Uncomment code bellow and make the file compilable")
-//    if (leftNode.value.upperBound < rightNode.value.lowerBound || leftNode.value.lowerBound > rightNode.value.upperBound) {
-//        return 0
-//    }
-//    return (leftNode.value.size + rightNode.value.size)/2
+    if (leftNode.value.upperBound < rightNode.value.lowerBound || leftNode.value.lowerBound > rightNode.value.upperBound) {
+        return 0
+    }
+    return (leftNode.value.size + rightNode.value.size)/2
 }
\ No newline at end of file
diff --git a/src/main/kotlin/exercise6/task4/UpperBoundConstraintPartThree.kt b/src/main/kotlin/exercise6/task4/UpperBoundConstraintPartThree.kt
index 4614d38..ef5d459 100644
--- a/src/main/kotlin/exercise6/task4/UpperBoundConstraintPartThree.kt
+++ b/src/main/kotlin/exercise6/task4/UpperBoundConstraintPartThree.kt
@@ -89,29 +89,27 @@ private data class SetIntersection<T: Comparable<T>>(
  * no intersection at all. If the intersection is likely to be not empty, it estimates the intersection size as the mean
  * of the set sizes.
  */
-private fun <T, S> estimateIntersectionSize(treeNode: TreeNode<T>) : Int {
-    TODO("Uncomment code bellow and make the file compilable")
-//    val leftNode = treeNode.left ?: return treeNode.value.size
-//    val rightNode = treeNode.right ?: return treeNode.value.size
-//
-//    if (leftNode.value.lowerBound == null || rightNode.value.lowerBound == null) {
-//        return 0
-//    }
-//    if (leftNode.value.upperBound == null || rightNode.value.upperBound == null) {
-//        return 0
-//    }
-//
-//    if (leftNode.value.upperBound!! < rightNode.value.lowerBound!! || leftNode.value.lowerBound!! > rightNode.value.upperBound!!) {
-//        return 0
-//    }
-//    return (leftNode.value.size + rightNode.value.size)/2
+private fun <T, S> estimateIntersectionSize(treeNode: TreeNode<T>) : Int where T: Range<S>, T: Measurable, S : Comparable<S>{
+    val leftNode = treeNode.left ?: return treeNode.value.size
+    val rightNode = treeNode.right ?: return treeNode.value.size
+
+    if (leftNode.value.lowerBound == null || rightNode.value.lowerBound == null) {
+        return 0
+    }
+    if (leftNode.value.upperBound == null || rightNode.value.upperBound == null) {
+        return 0
+    }
+
+    if (leftNode.value.upperBound!! < rightNode.value.lowerBound!! || leftNode.value.lowerBound!! > rightNode.value.upperBound!!) {
+        return 0
+    }
+    return (leftNode.value.size + rightNode.value.size)/2
 }
 
-private fun <T> printTree(treeNode: TreeNode<T>) {
-    TODO("Uncomment code bellow and make the file compilable")
-//    println("${treeNode.value} cost:${treeNode.value.cost}")
-//    treeNode.left?.let { printTree(it) }
-//    treeNode.right?.let { printTree(it) }
+private fun <T : CostElement> printTree(treeNode: TreeNode<T>) {
+    println("${treeNode.value} cost:${treeNode.value.cost}")
+    treeNode.left?.let { printTree(it) }
+    treeNode.right?.let { printTree(it) }
 }
 
 /**
@@ -148,12 +146,11 @@ private fun run() {
         it.left = leftNode
         it.right = rightNode
     }
-    TODO("Uncomment code bellow and make the file compilable")
-//    val intersectionSize = estimateIntersectionSize(rootNode)
-//    println(intersectionSize)
-//
-//    printTree(rootNode)
-//    printNodes()
+    val intersectionSize = estimateIntersectionSize(rootNode)
+    println(intersectionSize)
+
+    printTree(rootNode)
+    printNodes()
 }
 
 fun main() {
diff --git a/src/main/kotlin/exercise6/taskProjections/task1/Task.kt b/src/main/kotlin/exercise6/taskProjections/task1/Task.kt
index 7905d94..5d6d0cd 100644
--- a/src/main/kotlin/exercise6/taskProjections/task1/Task.kt
+++ b/src/main/kotlin/exercise6/taskProjections/task1/Task.kt
@@ -11,12 +11,12 @@ package exercise6.taskProjections.task1
 
 **/
 
-interface Sender {
-    fun send(item: Any)
+interface Sender<T>{
+    fun send(item: T)
 }
 
-class MailBox(private var box: Any? = null): Sender {
-    override fun send(item: Any) {
+class MailBox <T> (private var box: T? = null): Sender<T> {
+    override fun send(item: T) {
         printCurrentBoxState()
         println("Sending the box: $item!")
         box = item
@@ -32,8 +32,8 @@ class MailBox(private var box: Any? = null): Sender {
 
 }
 
-class Postman(private val mailboxes: List<Sender>): Sender {
-    override fun send(item: Any) {
+class Postman<T>(private val mailboxes: List<Sender<T>>): Sender<T> {
+    override fun send(item: T) {
         mailboxes.forEach { it.send(item) }
     }
 
@@ -45,14 +45,16 @@ open class Postcard(open val origin: String) : Delivery
 data class ExpressPostcard(val priceEuro: Int, override val origin: String) : Postcard(origin)
 
 fun main() {
-    // TODO: This code should became compilable
-//    val postcardStorage = MailBox<Postcard>()
-//    val expressPostcardStorage = MailBox<ExpressPostcard>()
+    val postcardStorage = MailBox<Postcard>()
+    val expressPostcardStorage = MailBox<ExpressPostcard>()
 
     val expressPostcard = ExpressPostcard(15, "Serbia")
     val postcard = Postcard("Germany")
 
-    // TODO: add code to create topRatedPostman and juniorPostman.
-    //  The topRatedPostman can send ONLY express postcards
-    //  The juniorPostman can send both regular and express postcards
+    val topRatedPostman: Postman<ExpressPostcard> = Postman(listOf(expressPostcardStorage))
+    val juniorPostman: Postman<Postcard> = Postman(listOf(postcardStorage))
+
+    topRatedPostman.send(expressPostcard)
+    juniorPostman.send(expressPostcard)
+    juniorPostman.send(postcard)
 }
\ No newline at end of file
diff --git a/src/main/kotlin/exercise6/taskProjections/task2/Task.kt b/src/main/kotlin/exercise6/taskProjections/task2/Task.kt
index b28c6ae..c95d203 100644
--- a/src/main/kotlin/exercise6/taskProjections/task2/Task.kt
+++ b/src/main/kotlin/exercise6/taskProjections/task2/Task.kt
@@ -10,6 +10,12 @@ package exercise6.taskProjections.task2
  * If you did everything correct, you could not create a method create which accepts nothing and returns T
 **/
 
+class Programmer<in T : ProgrammingLanguage>() {
+    fun learn(language: T) {
+        println("I learned ${language.name}!")
+    }
+}
+
 interface ProgrammingLanguage {
     val name: String
 }
@@ -18,16 +24,15 @@ class JvmLanguage(override val name: String) : ProgrammingLanguage
 class BlockBasedLanguage(override val name: String) : ProgrammingLanguage
 
 fun main() {
-    TODO("Uncomment this code when you finish the task")
-//    val programmer = Programmer<ProgrammingLanguage>()
-//
-//    val jvmLanguages = listOf(JvmLanguage("Java"), JvmLanguage("Kotlin"))
-//    jvmLanguages.forEach{ programmer.learn(it) } // OK
-//
-//    val blockBasedLanguages = listOf(BlockBasedLanguage("Scratch"), JvmLanguage("Snap"))
-//    blockBasedLanguages.forEach{ programmer.learn(it) } // OK
-//
-//    (jvmLanguages + blockBasedLanguages).forEach{ programmer.learn(it) } // OK
-//
-////    val newLanguage: ProgrammingLanguage = programmer.create() // ERROR
+    val programmer = Programmer<ProgrammingLanguage>()
+
+    val jvmLanguages = listOf(JvmLanguage("Java"), JvmLanguage("Kotlin"))
+    jvmLanguages.forEach{ programmer.learn(it) } // OK
+
+    val blockBasedLanguages = listOf(BlockBasedLanguage("Scratch"), JvmLanguage("Snap"))
+    blockBasedLanguages.forEach{ programmer.learn(it) } // OK
+
+    (jvmLanguages + blockBasedLanguages).forEach{ programmer.learn(it) } // OK
+
+//    val newLanguage: ProgrammingLanguage = programmer.create() // ERROR
 }
diff --git a/src/main/kotlin/exercise6/taskProjections/task3/Task.kt b/src/main/kotlin/exercise6/taskProjections/task3/Task.kt
index 211a74f..ce9c988 100644
--- a/src/main/kotlin/exercise6/taskProjections/task3/Task.kt
+++ b/src/main/kotlin/exercise6/taskProjections/task3/Task.kt
@@ -36,11 +36,12 @@ class BlockBasedLanguageParser : LanguageParser<BlockBasedLanguage> {
 }
 
 fun main() {
-    TODO("Create a new HashMap and uncomment code bellow")
-//    parsersHashMap[JvmLanguage::class.java] = JvmLanguageParser()
-//    parsersHashMap[BlockBasedLanguage::class.java] = BlockBasedLanguageParser()
-//
-//    val scratch = BlockBasedLanguage()
-//    val foundParser = parsersHashMap[scratch.javaClass]
-//    foundParser?.parse(scratch)
+    val parsersHashMap = HashMap<Class<*>, LanguageParser<*>>()
+
+    parsersHashMap[JvmLanguage::class.java] = JvmLanguageParser()
+    parsersHashMap[BlockBasedLanguage::class.java] = BlockBasedLanguageParser()
+
+    val scratch = BlockBasedLanguage()
+    val foundParser = parsersHashMap[scratch.javaClass]
+    foundParser?.parse(scratch)
 }
diff --git a/src/main/kotlin/exercise6/taskProjections/task4/Task.kt b/src/main/kotlin/exercise6/taskProjections/task4/Task.kt
index c2d86d9..0900516 100644
--- a/src/main/kotlin/exercise6/taskProjections/task4/Task.kt
+++ b/src/main/kotlin/exercise6/taskProjections/task4/Task.kt
@@ -7,6 +7,15 @@ package exercise6.taskProjections.task4
  * that accepts two arrays with a generic type of Any and copy elements from the first array to the second one.
 **/
 
+fun <Any> copy(arr1 : Array<Any>, arr2 : Array<in Any>) {
+    require(arr2.size >= arr1.size) {
+        throw Exception("Second array is shorter than first!")
+    }
+
+    for (i in arr1.indices)
+            arr2[i] = arr1[i]
+}
+
 fun main() {
     val ints = arrayOf(1, 2, 3)
     val any = Array<Any>(3) { "" }
@@ -17,8 +26,7 @@ fun main() {
     println("_______")
     println("_______")
 
-    // TODO: uncomment this code
-   // copy(ints, any)
+    copy(ints, any)
 
     ints.forEach{ print("$it ") }
     println()
diff --git a/src/main/kotlin/exercise6/taskProjections/task5/Task.kt b/src/main/kotlin/exercise6/taskProjections/task5/Task.kt
index 9123785..c7d8d72 100644
--- a/src/main/kotlin/exercise6/taskProjections/task5/Task.kt
+++ b/src/main/kotlin/exercise6/taskProjections/task5/Task.kt
@@ -7,6 +7,17 @@ package exercise6.taskProjections.task5
  * Create a new class "Printer", that can accept only T elements and print them
  *     - add a "print" function that prints item with type T;
  *
+
+ **/
+
+class Printer<T> {
+    fun print(element : T) {
+        println(element)
+    }
+}
+
+/**
+
  * [2]
  * Create a new abstract class "Builder" that generates instances of T based on parameter of P type.
  * This class cannot produce P and consume T:
@@ -14,20 +25,28 @@ package exercise6.taskProjections.task5
  * Create a new class "IntegerBuilder", that implements Builder and can convert String to Int
 **/
 
+abstract class Builder<in P, out T> {
+    abstract fun build(input : P) : T
+}
+
+class IntegerBuilder() : Builder<String, Int>() {
+    override fun build(input: String): Int {
+        return input.toInt()
+    }
+}
+
 fun main() {
     // [1]
-    // TODO: uncomment me
-//    val integerPrinter = Printer<Int>()
-//    val stringPrinter = Printer<String>()
-//
-//    integerPrinter.print(2)
-//    stringPrinter.print("Bla bla bla")
+    val integerPrinter = Printer<Int>()
+    val stringPrinter = Printer<String>()
+
+    integerPrinter.print(2)
+    stringPrinter.print("Bla bla bla")
 
     println("________")
 
     // [2]
-    // TODO: uncomment me
-//    val intBuilder = IntegerBuilder()
-//    val x = intBuilder.build("1")
-//    println("We build [ $x ]")
+    val intBuilder = IntegerBuilder()
+    val x = intBuilder.build("1")
+    println("We build [ $x ]")
 }
diff --git a/src/main/kotlin/exercise6/taskProjections/task6/Task.kt b/src/main/kotlin/exercise6/taskProjections/task6/Task.kt
index e897e4c..518fe1b 100644
--- a/src/main/kotlin/exercise6/taskProjections/task6/Task.kt
+++ b/src/main/kotlin/exercise6/taskProjections/task6/Task.kt
@@ -10,24 +10,22 @@ open class A
 class B : A()
 class C : A() { fun consume(other: A): C = this }
 
-// TODO: uncomment and fix me
-//fun <T, S : R, R> funny(
-//    source: Iterator<??>,
-//    target: MutableCollection<??>,
-//    base: ??,
-//    how: ??
-//) {
-//    var result: R = base
-//    for (value in source) {
-//        result = how(result, value)
-//        target.add(result)
-//    }
-//}
+fun <T, S : R, R> funny(
+    source: Iterator<T>,
+    target: MutableCollection<in R>,
+    base: R,
+    how: (R, T) -> S
+) {
+    var result: R = base
+    for (value in source) {
+        result = how(result, value)
+        target.add(result)
+    }
+}
 
 fun main() {
-    // TODO: uncomment me, it should not produce any compilation errors
-//    val wtf = mutableListOf<A>()
-//    val src = mapOf(3.14 to B(), 2 to B(), "Hello" to B())
-//    val c = C()
-//    funny(src.values.iterator(), wtf, c) { r, t -> r.consume(t) }
+    val wtf = mutableListOf<A>()
+    val src = mapOf(3.14 to B(), 2 to B(), "Hello" to B())
+    val c = C()
+    funny(src.values.iterator(), wtf, c) { r, t -> r.consume(t) }
 }