A 12-by-15 ft rectangular swimming pool has a 3-ft-wide no-slip surface around it. What is the outer perimeter of the no-slip surface?

1. Find the perimeter of the pool with the non-slip surface:

The swimming pool has a perimeter of 54 feet with the non-slip surface, found by the formula for the perimeter of a rectangle: 2l+2w=P

2. Find the perimeter of the pool without the non-slip surface:

To find the perimeter of the pool without the non-slip surface, subtract three feet from the length and the width, because the non-slip surface adds three feet to the width and the height. Then, use the new width and height (9 feet and 12 feet) to substitute into the perimeter formula.

2 (9) + 2 (12) = 42

3. Subtract the pool's perimeter without the non-slip surface from the pool's perimeter with the non-slip surface.

54 - 42 = 12

Twelve is the perimeter of the no-slip surface.