Find the sides of a rectangle if its length is 4 times its width and its perimeter is 90 cm.

To solve this problem, you must use the method of equations. Since if we enter a variable that will equal the value of the width, we can use the formula to find the perimeter of a rectangle to find the value of the length and width.

Let x be the width of the rectangle, then (4 * x) is its length. The perimeter of the rectangle is 2 * (x + 4 * x). We get the following equation:

2 * (x + 4 * x) = 90

2 * 5 * x = 90

10 * x = 90

x = 9 (centimeters) is the width of the rectangle.

9 * 4 = 36 (centimeters) – the length of the rectangle.

Answer: 36 centimeters and 9 centimeters.