c = 2*w*3 + 5 L = 6 w + 5 L
L = 120/w
so
c = 6 w + 600/w
dc/dw = 6 - 600/w^2 = 0 for min or max
w^2 = 100
w = 10
L = 12
Ann wants to build an enclosed area behind her house. One wall of the enclosed area will be the back of the house. She needs the total to be 120 sq feet. She wants to minimize the cost of fence materials. For the sides (W) fence materials cost $3/ft, for the length (L) they cost $5/ft. What dimensions should her fence be?
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