Find the width of the rectangle if its perimeter is 58 cm and its length is 18 cm.

The perimeter of a rectangle is equal to the sum of the lengths of all its sides.

Let us denote the perimeter of the rectangle by the letter “P”, its length by the letter “a”, and its width by the letter “b”.

Then the perimeter of the rectangle will be:

P = a + b + a + b = 2a + 2b = 2 * (a + b).

Knowing the perimeter of the rectangle and one of its sides, you can calculate the other side:

a = (P – 2b): 2;

b = (P – 2a): 2.

We calculate the width of a rectangle, the perimeter of which is 58 cm, and the length is 18 cm:

b = (58 – 2 * 18): 2 = (58 – 36): 2 = 22: 2 = 11 cm.

Answer: 11 cm.