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You have 96 feet of fencing to enclose a rectangle pan for your dog to provide sufficient running space
for your dog to exercise the pan should be three times as long as it is wide.
find the dimensions of the pen length and width
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If W is the width, then 3W is the length, and
W + 3W = 96/2 = 48, or
4W = 48,
W = 48/4 = 12 ft.
ANSWER. The dimensions should be 12 ft and 3*12 = 36 ft.
Solved.