Question

15 m
12 m
7 m
15 m
7 m
7 m
? m
72 - - - - - -

Explanation:

Step1: Sum known side lengths

$7 + 15 + 12 + 15 + 7 + 7 = 63$

Step2: Subtract sum from total perimeter

$72 - 63 = 9$

Answer:

$9$ m