Question 1021185
2w + l = 280
l = 280-2w
:
Area(A) = l * w
:
substitute for l in area equation
:
A = (280-2w) * w
A = 280w -2w^2
:
now take the first derivative of A
:
A' = 280 -4w
: 
set A' = 0 and solve for w
:
4w = 280
:
w = 70
l = 280 - 140 = 140
:
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length = 140 feet
width = 70 feet
area = 140 * 70 = 9800 square feet
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