Answer:
28
Explanation:
Since the perimeter is the width + width + length + length, we know that there 2 of the 8 millimeter width in the perimeter. So multiply 8 by 2, which is 16. So 16 of the 72 represents both widths. So subtract 16 from 72. You're left with 56, which represents 2 of the length. So divide 56 by 2, and you get one of the length, which is 28.