Each suma in simplest form

First compute the area of the square like this: 
There is two semi circles here, so the sum of the two white 
spaces equate the area of a circle. 
the radius of the circle is 9/2. 
So compute the area of the like this:  
And the area of the shaded region is the area of the square minus 
the area of the two semi circles, like this:

We are done.