First, we must understand that to find the perimeter of an object you must add up the lengths of each side.
Some options are:
A square (4 sides) with sides of 4 units long.
4x4=16
A rectangle (4 sides) that is 6 units long and 2 units wide
6+2+6+2=16
An octagon (8 sides) with sides 2 units long
8x2=16