The perimeter is the sum of the lengths of the four sides. Opposite sides have the same length, so it is twice the sum of the lengths of adjacent sides.
The sum of adjacent sides is (32 m)/2 = 16 m. If one of them is 11 m long, the other is ...
16 m - 11 m = 5 m
The "missing" side is 5 m long.
The length of the missing side is 5 m
In order to find this, use the perimeter formula.
P = 2L + 2W
Now input 11 as the L and 32 as P
32 = 2(11) + 2W
32 = 22 + 2W
10 = 2W
5 = W