9514 1404 393
Answer:
 17 ft, 27 ft, 20 ft
Step-by-step explanation:
Let s represent the length of the shortest side. The the longest side is (2s-7) and the third side is (s+3). The perimeter is the sum of the side lengths:
 64 = s +(2s -7) +(s +3)
 64 = 4s -4 . . . . . . . . . . . collect terms
 16 = s -1 . . . . . . . . . . divide by 4
 17 = s . . . . . . . . . add 1
 2s -7 = 2·17 -7 = 27 . . . . . the length of the longest side
 s +3 = 17 +3 = 20 . . . . . . . the length of the third side
The side lengths are 17 feet, 27 feet, and 20 feet.