Let L = Length, and W = Width. We are given the fact that L = 2W, and also know that the area = L x W = 50 square feet. So, by substitution: 2W x W = 50 sq ft, or 2W^2 = 50 sq ft, so W = sq rt (50/2) = 5 ft. Now, L = 2W = 2(5) = 10 ft. The perimeter of the fence is given by: 2L + 2W = 2(10 ft) + 2(5 ft) =20 ft + 10 ft = 30 ft. So, Ben needs 30 ft of fencing.
