Write a ratio in simplified form of the area of the shaded figure to the area of the figure that encloses it.

First, let's start by finding the Areas for both shaded and not shaded.

-Area of the shaded area = Length²
Area of the shaded area = 6² = 36
-Area of the not shaded region =  
Area of the not shaded region = 
                                                    = 
                                                    = 15
Now, Let's make our ration!
Area of shaded : Area of not shaded
           36            :               15
           12             :                5