P = 2L + 2W



You are given L=12in and P=6L:



6L = 2L + 2W

4L = 2W

4*12 = 2W



W = 24in   





Check (calculate Perimeter both ways):



P = 2L + 2W = 2*12 + 2*24 = 24 + 48 = 72

P = 6L = 6*12 = 72  (ok) 

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