diff --git a/lib/problems.js b/lib/problems.js
index 0c3ab21..275311f 100644
--- a/lib/problems.js
+++ b/lib/problems.js
@@ -1,18 +1,98 @@
+const Stack = require("./stack");
+const Queue = require("./queue");
+
 /*
-Time Complexity: ?
-Space Complexity: ?
+Time Complexity: O(n)
+Space Complexity: O(n)
 */
 const balanced = (str) => {
-    throw new Error("This method has not been implemented!");
+    const stack = new Stack;
+    const OPENING_BRACES = ['[', '{', '('];
+    const CLOSING_BRACES = [']', '}', ')'];
+    let prevChar = null;
+
+    for(let i = 0; i < str.length; i++) {
+        const newChar = str.charAt(i);
+        prevChar = stack.peek();
+
+        stack.push(newChar);
+
+        if (CLOSING_BRACES.includes(newChar)) {
+            switch(newChar){
+                case CLOSING_BRACES[0]:
+                    if (prevChar == OPENING_BRACES[0]) {
+                        stack.pop();
+                        stack.pop();
+                    }
+                    break;
+                case CLOSING_BRACES[1]:
+                    if (prevChar == OPENING_BRACES[1]) {
+                        stack.pop();
+                        stack.pop();
+                    }
+                    break;
+                case CLOSING_BRACES[2]:
+                    if (prevChar == OPENING_BRACES[2]) {
+                        stack.pop();
+                        stack.pop();
+                    }
+                    break;
+            }
+        }
+    }
+
+    return stack.isEmpty();
 }
 
 /*
-Time Complexity: ?
-Space Complexity: ?
+Time Complexity: O(n) 
+Space Complexity: O(n)
 */
 const evaluatePostfix = (expr) => {
-    throw new Error("This method has not been implemented!");
+    const OPERATORS = ['+', '-', '*', '/'];
+    const operandsQueue = new Queue;
+    const operatorsQueue = new Queue;
+    let result = null;
+    let operand1 = null;
+
+    for(let i = 0; i < expr.length; i++) {
+        const currentChar = expr.charAt(i);
+        if (OPERATORS.includes(currentChar)) {
+            operatorsQueue.enqueue(currentChar);
+        } else {
+            operandsQueue.enqueue(parseInt(currentChar));
+        }
+    }
+
+    const numOperators = operatorsQueue.length();
+
+    for(let i = 0; i < numOperators; i++) {
+        if (operand1 == null) {
+            operand1 = operandsQueue.dequeue();
+        } else {
+            operand1 = result;
+        }
+        let operator = operatorsQueue.dequeue();
+        let operand2 = operandsQueue.dequeue();
+        result = evaluateOperands(operator, operand1, operand2);
+    }
+
+    return result;
 }
 
+function evaluateOperands(operator, operand1, operand2) {
+    switch (operator) {
+        case '+':
+            return operand1 + operand2;
+        case '-':
+            return operand1 - operand2;
+        case '*':
+            return operand1 * operand2;
+        case '/':
+            return parseInt(operand1 / operand2);
+    }
+}
+
+
 exports.balanced = balanced;
 exports.evaluatePostfix = evaluatePostfix;
diff --git a/lib/queue.js b/lib/queue.js
index 7a653f8..e39ef60 100644
--- a/lib/queue.js
+++ b/lib/queue.js
@@ -1,27 +1,56 @@
+//Using a circular buffer with an internal array starting at 20 elements
+
 class Queue {
     constructor() {
-        // this.store = ...
-        throw new Error("This method has not been implemented!");
+        this.store = new Array(20);
+        this.front = 0;
+        this.rear = 0;
     }
 
-    enqueue(element) {
-        throw new Error("This method has not been implemented!");
+    enqueue(value) {
+        if (this.rear == (this.size() - 1)) {
+            this.rear = 0;
+        } else {
+            this.rear++;
+        }
+        this.store[this.rear] = value;
     }
 
     dequeue() {
-        throw new Error("This method has not been implemented!");
+        if (this.front == (this.size() - 1)) {
+            this.front = 0;
+        } else {
+            this.front++;
+        }
+
+        const dequeued = this.store[this.front];
+        this.store[this.front] = null;
+
+        return dequeued;
     }
 
     front() {
-        throw new Error("This method has not been implemented!");
+        return this.store[front];
     }
 
     size() {
-        throw new Error("This method has not been implemented!");
+        let count = 0;
+        while (!!this.store[count]) {
+            count++;
+        }
+        return count;
+    }
+
+    length() {
+        return this.rear - this.front;
     }
 
     isEmpty() {
-        throw new Error("This method has not been implemented!");
+        if (this.front == this.rear) {
+            return true;
+        } else {
+            return false;
+        }
     }
 
     toString() {
diff --git a/lib/stack.js b/lib/stack.js
index dff9f6c..699466c 100644
--- a/lib/stack.js
+++ b/lib/stack.js
@@ -1,19 +1,31 @@
+const LinkedList = require("./linked-list");
+
 class Stack {
     constructor() {
-        // this.store = ...
-        throw new Error("This method has not been implemented!");
+        this.store = new LinkedList;
     }
 
-    push() {
-        throw new Error("This method has not been implemented!");
+    push(value) {
+        this.store.addLast(value);
+        return this.store.getLast();
     }
 
     pop() {
-        throw new Error("This method has not been implemented!");
+        const popped = this.store.getLast();
+        this.store.delete(popped);
+        return popped;
+    }
+
+    peek() {
+        return this.store.getLast();
     }
 
     isEmpty() {
-        throw new Error("This method has not been implemented!");
+        if (this.store.length() == 0) {
+            return true;
+        } else {
+            return false;
+        }
     }
 
     toString() {
diff --git a/test/problems.test.js b/test/problems.test.js
index a14ff20..749ee8c 100644
--- a/test/problems.test.js
+++ b/test/problems.test.js
@@ -43,4 +43,4 @@ describe("test wave 3 problems", () => {
             expect(evaluatePostfix('62/5+')).toEqual(8);
         });
     });
-});
\ No newline at end of file
+});
diff --git a/test/queue.test.js b/test/queue.test.js
index e1bec8c..353f117 100644
--- a/test/queue.test.js
+++ b/test/queue.test.js
@@ -101,4 +101,4 @@ describe("test queue implementation", () => {
         expect(q.toString()).toEqual('[40,50,60,70,80,90,100,110,120,130,140,150,160,170,180,190,200,210]');
     });
 
-});
\ No newline at end of file
+});
diff --git a/test/stack.test.js b/test/stack.test.js
index 6d5dbf5..9ef2dba 100644
--- a/test/stack.test.js
+++ b/test/stack.test.js
@@ -43,4 +43,4 @@ describe('test stack implementation', () => {
         const removed = stack.pop();
         expect(removed).toEqual(7);
     });
-});
\ No newline at end of file
+});