Answer:
12
Step-by-step explanation:
if the perimeter is 54, and the length is 15,
first double the length (to include both sides of the rectangle):
15(2)=30
subtract that by 54:
54-30=24
to find the width we would divide 24 by 2, because 24 represents both sides of the rectangle:
24/2=12
the width is 12.
