The perimeter is P = 2L + 2W or 80 = 2L + 2W dividing by 2 we get 40 = L + W THe area is
A = LW solving for L, we get L = 40-W substituting that in , we get A = (40-W)(W) using completing the square, we get A = -(W-20)^2 + 400 So, when W = 20, the max area is 400.
