#### Answer

The perimeter is 142 m

#### Work Step by Step

The left side has a length of 31 - 6 = 25m
The upper unknown side has a length of 20-15 = 5m
The perimeter is equal to the sum of the lengths of its sides
perimeter = 15 + 31 + 20 + 6 + 5 + 25
perimeter = 142