diff --git a/lib/problems.rb b/lib/problems.rb
index 5085953d..83778701 100644
--- a/lib/problems.rb
+++ b/lib/problems.rb
@@ -1,13 +1,27 @@
 require_relative './stack.rb'
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  return false if string.length.odd?
+  brackets = {"{" => "}", "[" => "]", "(" => ")"}
+  bracket_stack = Stack.new
+  # for each char, if bracket, push it into stack
+  string.chars.each do |char|
+    if brackets[char]
+      bracket_stack.push(brackets[char])
+    else # pop last item, see if it matches char, and if not return false
+      if bracket_stack.pop != char
+        return false
+      end
+    end
+  end
+  return bracket_stack.empty? # must be empty to return true
 end
 
 # Time Complexity: ?
 # Space Complexity: ?
 def evaluate_postfix(postfix_expression)
   raise NotImplementedError, "Not implemented yet"
+  # new stack
 end
diff --git a/lib/queue.rb b/lib/queue.rb
index 828217c6..8a059dbf 100644
--- a/lib/queue.rb
+++ b/lib/queue.rb
@@ -1,31 +1,50 @@
-class Queue
-
+class Queue # FIFO; Elements added to the rear and removed from front
+# An Abstract Data Type is a data type with a specific public interface, but unspecified implementation.
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = Array.new(20)
+    @size = 20
+    @front = 0
+    @back = 0
+    
   end
 
-  def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+  def enqueue(element) # add an element to the rear of the queue
+    if @front == (@back + 1) % size
+      raise ArgumentError, "Queue is full"
+    else # move back to next position clockwise
+      @store[@back] = element
+      @back = (@back + 1) % @size
+    end
   end
 
-  def dequeue
-    raise NotImplementedError, "Not yet implemented"
+  def dequeue # Remove & return the element from the front
+    if @front == @back
+      raise ArgumentError, "Queue is empty"
+    else # move front to next position clockwise
+      result = @store[@front]
+      @front = (@front + 1) % @size
+      return result
+    end
   end
 
   def front
-    raise NotImplementedError, "Not yet implemented"
+    return @store[@front]
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    return @store.size
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @front == @back
   end
 
   def to_s
-    return @store.to_s
+    result = []
+    @store.each do |element|
+      result << element if element
+    end
+    return result.to_s
   end
+
 end
diff --git a/lib/stack.rb b/lib/stack.rb
index cfc6ef0f..0a0c2fb7 100644
--- a/lib/stack.rb
+++ b/lib/stack.rb
@@ -1,19 +1,19 @@
 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 self.empty?
+    @store.remove_first()
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+   @store.empty?
   end
 
   def to_s
diff --git a/test/problems_test.rb b/test/problems_test.rb
index 046f059e..694262b8 100644
--- a/test/problems_test.rb
+++ b/test/problems_test.rb
@@ -2,7 +2,7 @@
 
 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
       
@@ -33,7 +33,7 @@
     end
   end
 
-  describe "postfix" do
+  xdescribe "postfix" do
     it "can add a 2 numbers together" do
       
       expect(evaluate_postfix("34+")).must_equal 7
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 426168c8..6dfc6980 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -9,5 +9,4 @@
 require_relative "../lib/linked_list.rb"
 require_relative "../lib/queue.rb"
 require_relative "../lib/stack.rb"
-# Extra exercises
-# require_relative "../lib/problems.rb"
\ No newline at end of file
+require_relative "../lib/problems.rb"
\ No newline at end of file