Answer:
39 ft^2
Explanation:
Find the area of the triangle and subtract the area of the square.
area of triangle = bh/2
area of square = s^2
shaded area = bh/2 - s^2
shaded area = (20 ft)(16 ft)/2 - (11 ft)^2
shaded area = 160 ft^2 - 121 ft^2
shaded area = 39 ft^2