Question 794816
Width = x feet
Length = 200 - 2x
Area = x(200 - 2x)
Area(x)= 200x - 2x^2
Area'(x) = 200 - 4x
A(x) = 0
200 - 4x = 0
-4x = -200
 x = 50
Using Nature Table:
 ................ -     50    +
200 - 4x... +     0     -
So, x = 50 feet is a maximum.
Width = 50 feet
Length = 100 feet
Area = 50*100 = 5000 feet.
Hope this helps.
:-)