Answer:
let the shortest side be 'x' ft
length of second side = x + 6 ft
length of third side = 2(x+6) - 6 ft
perimeter of triangle = 72 feet
shortest side + second side + third side = 72 ft
x + x + 6 + 2(x+6) - 6 = 72
4x + 12 = 72
x = 15
length of shortest side = 15 ft
length of second side = 15 + 6 = 21 ft
length of third side = 2(15 + 6) - 6 = 36 ft