the perimeter of a school crossing sign is 102 inches what is the length of each side

Add up all sides lengths:

s+6  +    s+6    +  s  +    s    + 2s    = 102

solve for s:

6s + 12 = 102
6s = 90
s= 15


The lengths of sides are as follows:

15, 21, 21, 15, 30 inches



I hope that helps!