1. how do i find the area of the shaded region?
2. how much does the concrete cost for the foundation?

Area of the triangle is base x height, divided by 2, so that is (8 x 10= 80 divided by 2, which is 40.
area of the rectangle is base x height, so that is 3x2= 6
so 40-6 is the area of the shaded region.
so 34 meters squared is your answer.

(length x width x height) x 4$
  (16 x 14 x 3) x 4 = cost
  cost = 2688$