The lines drawn on the perimeter indicate that the lengths are the same so the single line indicates it is the same length as the 5 ft line, etc... so there is one 3 ft, two 5 ft, two 3.5 ft, and two 6 ft I inescapable in the perimeter.
3 + 2 (5) + 2 (3.5) + 2 (6) =
3 + 10 + 7 + 12 =
32
The perimeter is 32 ft