Question 460980
2x+2y=160

160-2x = 2y
80-x = y

xy=A

x(80-x)=A
80x-x^2=A

Find gradient when zero ie the peak.

80-2x=0

x=80/2
x=40

So maximum area is 80*40-40^2 = 1600 square feet.

Width is 1600/40 = 40