Area of a triangle: 1/2 of area*height
(4*4)/2
16/2 = 8
8 * 4, since there are 4 triangles. = 32
18 * 8 (for the square) = 144
144 - 32 = 112 inches squared.
The triangles aren't shaded, so you can subtract them from the area of the rectangle to get the shaded area. The answer is 112 inches squared.
