Explanation:
the outer left side is also 50 ft.
in inner (upper) left side is also 13 ft.
the bottom line is 10+20+11 = 41 ft
this is all possible because all the angles are clearly right angles (90°).
so, the perimeter is
2×(10+20+11) + 2×50 + 2×13 = 82 + 100 + 26 = 208 ft