The perimeter of the rectangle is 18 cm and one side is 4 cm, find the second side of the rectangle.

Let’s find the unknown side of the rectangle, provided that the sum of all its sides is 18 cm, and the width = 4 cm.

The perimeter of such a figure is calculated by the formula:

P = 2a + 2b.

Substitute the known values and write the equation:

2a + 2 * 4 = 18.

2a + 8 = 18. We leave the variable with the coefficient on the left side of the equation, and transfer the number to the right side, while changing the sign in front of it to the opposite:

2a = 18 – 8 = 10.

To find the second factor, divide the product by the first:

a = 10: 2 = 5 cm – length.