And explain how to find out the answer

The area of the rectangle is base x height, which would be 12 x 17 = 204. 
The area of a triangle is (½)base x height. Since the top of the rectangle is 12 inches, and the bottom part is 16 inches including the base of the triangle, you can do 16 - 12 = 4 (which is the base of the triangle). The same thing with the sides of the rectangle. The whole side of the rectangle is 17 inches, and the other side is 11 inches. The height of the triangle then is 17 - 11 = 6 inches. The area of the triangle is ½ x 4 x 6 = 12. You add the area of the triangle and the rectangle to get 12 + 204 = 216 in^2. 

Suma 12+11+17+16 y eso da 56 dividelo por 2 eso da 28
la formula es A=bh÷2
12+11+17+16=56
56÷2=28
the answer is 28 suerte espero entiendas