The area of the rectangle is 120 cm square, the length of one of its sides is 15 cm, the perimeter of this rectangle was calculated.

1. Let:

a = 15 cm and b – sides of the rectangle;
S = 120 cm ^ 2 – area of the rectangle;
P is its perimeter.
2. The area of a rectangle is equal to the product of two sides:

S = ab,

from here we find the unknown side:

b = S: a = 120: 15 = 8 (cm).

3. The perimeter of the rectangle is equal to the sum of the four sides:

P = 2a + 2b = 2 (a + b) = 2 (15 + 8) = 2 * 23 = 46 (cm).

Answer. The perimeter of the rectangle is 46 cm.