The length of the rectangle, the perimeter of which is 20 cm, is equal to 7 cm, which is equal to its width.

A rectangle is a quadrilateral with opposite sides parallel to one another and equal in size, the angles are all 90 °.

The perimeter of a rectangle is equal to the sum of all its sides, that is, two widths (a) and two lengths (b) must be added.

We use the perimeter formula:

P = (a + b) x 2.

In our example, P = 20 cm, h = 7 cm, we find side a:

20 = (a + 7) x 2, 20/2 = a + 7, 10 = a + 7, hence a = 10 – 7 = 3 cm.

Thus, the width of the rectangle is 3 cm.