diff --git a/lib/problems.rb b/lib/problems.rb
index 5085953d..9f2d528c 100644
--- a/lib/problems.rb
+++ b/lib/problems.rb
@@ -1,13 +1,32 @@
 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 % 2 != 0
+  
+  struct = Stack.new
+  left_half = ["(", "[", "{"]
+  right_half = [")", "]", "}"]
+
+  left = 0
+  right = string.length - 1
+  until left >= right
+    index = left_half.find_index { |el| el == string[left] }
+
+    if !index.nil? && string[right] != right_half[index]
+      return false if string[left + 1] != right_half[index]
+    end
+    
+    left += 1
+    right -= 1
+  end
+
+  true
 end
 
 # Time Complexity: ?
 # Space Complexity: ?
-def evaluate_postfix(postfix_expression)
-  raise NotImplementedError, "Not implemented yet"
-end
+# def evaluate_postfix(postfix_expression)
+#   raise NotImplementedError, "Not implemented yet"
+# end
diff --git a/lib/queue.rb b/lib/queue.rb
index 828217c6..8eb047e7 100644
--- a/lib/queue.rb
+++ b/lib/queue.rb
@@ -1,31 +1,50 @@
 class Queue
-
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = Array.new
+    @size = 20
+    @first = 0
+    @last = 0
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    return nil if @first == (@last + 1) % @size
+
+    @store[@last] = element
+    @last = (@last + 1) % @size
   end
 
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    return nil if self.empty?
+
+    element = @store[@first]
+    @first = (@first + 1) % size
+
+    return element
   end
 
-  def front
-    raise NotImplementedError, "Not yet implemented"
+  def first
+    @store[@first]
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    return @size
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @first == @last
   end
 
   def to_s
-    return @store.to_s
+    return nil if self.empty?
+
+    string_queue = Array.new
+    current_element = @first
+
+    until current_element == @last
+      string_queue << @store[current_element]
+      current_element = (current_element + 1) % @size
+    end
+
+    return string_queue.to_s
   end
 end
diff --git a/lib/stack.rb b/lib/stack.rb
index cfc6ef0f..d0314d43 100644
--- a/lib/stack.rb
+++ b/lib/stack.rb
@@ -1,19 +1,21 @@
+require_relative './linked_list.rb'
+
 class Stack
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    @store.add_last(element)
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    return nil if self.empty?
+    element = @store.remove_last
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @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..f9340080 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -10,4 +10,4 @@
 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