the fence around a rectangular compound costs $4 a foot for three of the four sides. the fourth side is the wall of a building, so no fence is needed for that side. we will call the distance of the fence parallel to the wall w for width and the two other sides d for depth.
a) write the cost C in terms of w and d
answer: 2d+w=C
b) assume the cost is fixed at $400. write d in terms of w.
answer: w=400-2d
c) the area is w*d. write area as A(w).
answer: d(400-2d)= 400d-2d^2
not sure if my answers are correct