let w be the width of the rectangle and
l be the length of the rectangle.
Then the area is calculated by:
the fence f consists of . Since f = 480 you get:
Plug in the term for l into the equation :
This is a parabola opening downward, the maximum value is at it's vertex:
You'll get: w = 120 m and l = 240 m. The maximum area is 28800 mē