diff --git a/.vscode/launch.json b/.vscode/launch.json
new file mode 100644
index 00000000..dbfd5530
--- /dev/null
+++ b/.vscode/launch.json
@@ -0,0 +1,16 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "type": "ruby-debug",
+            "request": "launch",
+            "name": "Launch File",
+            "program": "${workspaceFolder}/${command:AskForProgramName}",
+            "programArgs": [],
+            "useBundler": false
+        }
+    ]
+}
\ No newline at end of file
diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index edd32b4d..a62f49ba 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -339,4 +339,4 @@ def to_s
 
       return list.to_s
     end
-end
+end
\ No newline at end of file
diff --git a/lib/problems.rb b/lib/problems.rb
index 5085953d..7bcf1cc2 100644
--- a/lib/problems.rb
+++ b/lib/problems.rb
@@ -1,13 +1,59 @@
 require_relative './stack.rb'
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  open = {
+    "(" => true,
+    "{" => true,
+    "[" => true
+  }
+
+  close = {
+    ")" => "(",
+    "}" => "{",
+    "]" => "["
+  }
+
+  results = Stack.new
+
+  string.each_char do |char|
+    if open[char]
+      results.push(char)
+    elsif close[char]
+      return false if results.pop != close[char]
+    end
+  end
+
+  results.empty?
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def evaluate_postfix(postfix_expression)
-  raise NotImplementedError, "Not implemented yet"
+  stack = []
+  math = '*+/-'
+
+  postfix_expression.each_char do |char|
+    if math.include?char
+      num2 = stack.pop
+      num1 = stack.pop
+      stack << calculator(num1, num2, char)
+    else
+      stack << char.to_i
+    end
+  end
+  stack.pop
 end
+
+def calculator(num1,num2,operator)
+  if operator == '+'
+    num1 + num2
+  elsif operator == '-'
+    num1 - num2
+  elsif operator == '*'
+    num1 * num2
+  elsif operator == '/'
+    num1/num2
+  end
+end
\ No newline at end of file
diff --git a/lib/queue.rb b/lib/queue.rb
index 828217c6..e86708ef 100644
--- a/lib/queue.rb
+++ b/lib/queue.rb
@@ -1,31 +1,64 @@
 class Queue
+  Array_Length = 20
 
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = Array.new(Array_Length)
+    @front = @back = 0 # back is the LAST EMPTY Space at the end
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    if @front.nil? 
+      @front = @back = 0
+    elsif @front - @back == 1 || (@back - @front == Array_Length - 1) # edge case were @back and @front are in different sides of the circle
+      raise ArgumentError, 'Queue is full' 
+    end
+
+    @store[@back] = element
+    @back = (@back + 1) % Array_Length # to update the back
+
   end
 
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    if @front == @back || @front.nil?
+      raise ArgumentError, 'Queue is empty'
+    end
+
+    temp = @store[@front]
+    @front = (@front + 1) % Array_Length
+    return temp
   end
 
   def front
-    raise NotImplementedError, "Not yet implemented"
+    return @store[@front]
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    return 0 if @front.nil?
+    if @front < @back
+      @back - @front
+    else
+      Array_Length - (@front + @back)
+    end
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    if @front.nil? || @front == @back
+      return true
+    else
+      return false
+    end
   end
 
   def to_s
-    return @store.to_s
+    results = []
+    if @back >= @front 
+      results = @store[@front...@back]
+    else
+      # from beginig to end of the list + begining to @back
+      results = @store[@front...Array_Length] + (@store[0...@back]) 
+    end
+    return results.to_s
   end
+
+
 end
diff --git a/lib/stack.rb b/lib/stack.rb
index cfc6ef0f..d8b3b9ed 100644
--- a/lib/stack.rb
+++ b/lib/stack.rb
@@ -1,22 +1,24 @@
 class Stack
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    @store.add_first(element)
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    return nil if @store.empty?
+    @store.remove_first
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return true if @store.empty?
+    return false
   end
 
   def to_s
     return @store.to_s
   end
-end
+  
+end
\ No newline at end of file
diff --git a/test/problems_test.rb b/test/problems_test.rb
index 046f059e..f28aff57 100644
--- a/test/problems_test.rb
+++ b/test/problems_test.rb
@@ -1,8 +1,9 @@
 require_relative 'test_helper'
+require_relative '../lib/problems'
 
 Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
 
-xdescribe "Test wave 3 problems" do
+describe "Test wave 3 problems" do
   describe "balanced" do
     it "Given balanced strings it should return true" do
       
diff --git a/test/queue_test.rb b/test/queue_test.rb
index 92fc11fb..a6a0b74f 100644
--- a/test/queue_test.rb
+++ b/test/queue_test.rb
@@ -25,6 +25,15 @@
     expect(q.to_s).must_equal "[10, 20, 30]"
   end
 
+  it "returns the correct size of the queue" do
+
+    q = Queue.new
+    q.enqueue(1)
+    q.enqueue(2)
+    q.enqueue(3)
+    expect(q.size).must_equal 3
+  end
+
   it "starts the Queue empty" do
     
     q = Queue.new