A rectangular pool has a tile border around its perimeter that measures 66 feet. If the length of the pool is 18 feet, what is the width of the pool?

Perimeter = side1 + side2 + side3 + side4

Retangular means side1=side3 and side2=side4 so

66 = 2*side1 + 2*side2

Side 1 = 18 feet so

66 = 2*18 + 2*side2

66 = 36 + 2*side2

33=18+side2

33-18=side2

15 = side2

The pool is 15 feet wide. Checking 15+15+18+18=66