The area of the rectangle is 64 cm, its width is 4 cm, find the perimeter of the rectangle.

First of all, we express the length of the rectangle, from the formula for determining the area of such a figure:
S = a * b, therefore: b = S: a. From the condition we know that S is 64 cm² and width = 4 cm:
b = 64: 4 = 16 cm.
The sum of all sides of the rectangle (perimeter) corresponds to the formula:
P = 2a + 2b = 2 * 16 + 2 * 4 = 32 + 8 = 40 cm.