Let s represent the length of the shortest side. Then the middle length side is (2s+4) and the longest side is (3s-4). The perimeter is the sum of the side lengths:
54 = s +(2s +4) +(3s -4)
54 = 6s . . . . . . . . . . . . . . collect terms
9 = s . . . . . . . . . . divide by 6
2s+4 = 2·9 +4 = 22
3s -4 = 3·9 -4 = 23
The lengths of the three sides are 9 feet, 22 feet, and 23 feet.
