diff --git a/Standard/estimated-time-to-review/file1.js b/Standard/estimated-time-to-review/file1.js
new file mode 100644
index 0000000..917a203
--- /dev/null
+++ b/Standard/estimated-time-to-review/file1.js
@@ -0,0 +1,47 @@
+const readline = require('readline');
+
+const rl = readline.createInterface({
+    input: process.stdin,
+    output: process.stdout
+});
+
+
+const performCalculation = (num1, operator, num2) => {
+    num1 = parseFloat(num1);
+    num2 = parseFloat(num2);
+
+    let result;
+    switch (operator) {
+        case '+':
+            result = num1 + num2;
+            break;
+        case '-':
+            result = num1 - num2;
+            break;
+        case '*':
+            result = num1 * num2;
+            break;
+        case '/':
+            if (num2 !== 0) {
+                result = num1 / num2;
+            } else {
+                console.log("Error! Division by zero is not allowed.");
+                return;
+            }
+            break;
+        default:
+            console.log(`Unknown operator '${operator}'. Please use one of the following: +, -, *, /`);
+            return;
+    }
+
+    console.log(`The result of ${num1} ${operator} ${num2} is ${result}`);
+};
+
+rl.question('Enter the first number: ', (answer1) => {
+    rl.question('Enter the operator (+, -, *, /): ', (operator) => {
+        rl.question('Enter the second number: ', (answer2) => {
+            performCalculation(answer1, operator, answer2);
+            rl.close();
+        });
+    });
+});
diff --git a/Standard/estimated-time-to-review/file2.js b/Standard/estimated-time-to-review/file2.js
new file mode 100644
index 0000000..46247aa
--- /dev/null
+++ b/Standard/estimated-time-to-review/file2.js
@@ -0,0 +1,46 @@
+const readline = require('readline');
+
+const rl = readline.createInterface({
+    input: process.stdin,
+    output: process.stdout
+});
+
+const performCalculation = (num1, operator, num2) => {
+    num1 = parseFloat(num1);
+    num2 = parseFloat(num2);
+
+    let result;
+    switch (operator) {
+        case '+':
+            result = num1 + num2;
+            break;
+        case '-':
+            result = num1 - num2;
+            break;
+        case '*':
+            result = num1 * num2;
+            break;
+        case '/':
+            if (num2 !== 0) {
+                result = num1 / num2;
+            } else {
+                console.log("Error! Division by zero is not allowed.");
+                return;
+            }
+            break;
+        default:
+            console.log(`Unknown operator '${operator}'. Please use one of the following: +, -, *, /`);
+            return;
+    }
+
+    console.log(`The result of ${num1} ${operator} ${num2} is ${result}`);
+};
+
+rl.question('Enter the first number: ', (answer1) => {
+    rl.question('Enter the operator (+, -, *, /): ', (operator) => {
+        rl.question('Enter the second number: ', (answer2) => {
+            performCalculation(answer1, operator, answer2);
+            rl.close();
+        });
+    });
+});
diff --git a/Standard/estimated-time-to-review/file3.js b/Standard/estimated-time-to-review/file3.js
new file mode 100644
index 0000000..46247aa
--- /dev/null
+++ b/Standard/estimated-time-to-review/file3.js
@@ -0,0 +1,46 @@
+const readline = require('readline');
+
+const rl = readline.createInterface({
+    input: process.stdin,
+    output: process.stdout
+});
+
+const performCalculation = (num1, operator, num2) => {
+    num1 = parseFloat(num1);
+    num2 = parseFloat(num2);
+
+    let result;
+    switch (operator) {
+        case '+':
+            result = num1 + num2;
+            break;
+        case '-':
+            result = num1 - num2;
+            break;
+        case '*':
+            result = num1 * num2;
+            break;
+        case '/':
+            if (num2 !== 0) {
+                result = num1 / num2;
+            } else {
+                console.log("Error! Division by zero is not allowed.");
+                return;
+            }
+            break;
+        default:
+            console.log(`Unknown operator '${operator}'. Please use one of the following: +, -, *, /`);
+            return;
+    }
+
+    console.log(`The result of ${num1} ${operator} ${num2} is ${result}`);
+};
+
+rl.question('Enter the first number: ', (answer1) => {
+    rl.question('Enter the operator (+, -, *, /): ', (operator) => {
+        rl.question('Enter the second number: ', (answer2) => {
+            performCalculation(answer1, operator, answer2);
+            rl.close();
+        });
+    });
+});
diff --git a/Standard/estimated-time-to-review/file4.js b/Standard/estimated-time-to-review/file4.js
new file mode 100644
index 0000000..46247aa
--- /dev/null
+++ b/Standard/estimated-time-to-review/file4.js
@@ -0,0 +1,46 @@
+const readline = require('readline');
+
+const rl = readline.createInterface({
+    input: process.stdin,
+    output: process.stdout
+});
+
+const performCalculation = (num1, operator, num2) => {
+    num1 = parseFloat(num1);
+    num2 = parseFloat(num2);
+
+    let result;
+    switch (operator) {
+        case '+':
+            result = num1 + num2;
+            break;
+        case '-':
+            result = num1 - num2;
+            break;
+        case '*':
+            result = num1 * num2;
+            break;
+        case '/':
+            if (num2 !== 0) {
+                result = num1 / num2;
+            } else {
+                console.log("Error! Division by zero is not allowed.");
+                return;
+            }
+            break;
+        default:
+            console.log(`Unknown operator '${operator}'. Please use one of the following: +, -, *, /`);
+            return;
+    }
+
+    console.log(`The result of ${num1} ${operator} ${num2} is ${result}`);
+};
+
+rl.question('Enter the first number: ', (answer1) => {
+    rl.question('Enter the operator (+, -, *, /): ', (operator) => {
+        rl.question('Enter the second number: ', (answer2) => {
+            performCalculation(answer1, operator, answer2);
+            rl.close();
+        });
+    });
+});