Answer:
2
Step-by-step explanation:
lucky guess from my boi tony
Width=w
length=(40-2w)/2=20-w
A=w(40-w)
A=40w-w²
A'=40-2w=0
2w=40
w=20
20x20 is the size of the pen having the greatest area. this tells us the largest rectangle for a given perimeter is a square
