Because it is a rectangle, the area is expressed as A = xy, or length times width. Because it is next to the river, he only needs to fence three sides, so F = x + 2y. Knowing the amount of fencing available is 7500m, we get: 7500 = x + 2y solve for x x = 7500 - 2y substitute into the area equation A = (7500 - 2y)y distribute A = -2y2 +7500y You can see that this is a parabola which opens down, meaning that the point of maximum area will be at the vertex, y = -b/2a = -7500/[2(-2)] = 1875 x = 7500 - 2(1875) = 3750 A = 3750(1875) = 7,031,250 m2