The length of the rectangle is 2 times its width, and its perimeter is 138 cm.

From the condition it is known that the length of the rectangle is 2 times greater than the width, and it is also known that its perimeter is 138 cm.To find the lengths of the sides of the rectangle, we will compose and solve a linear equation using the formula for finding the perimeter of a rectangle.

P = 2 (a + b).

Let’s denote by x cm the width of the rectangle, then the length of the rectangle can be written as 2x.

We substitute in the formula for calculating the perimeter:

2 (x + 2x) = 138;

x + 2x = 138: 2;

3x = 69;

x = 69: 3;

x = 23 cm width and 23 * 2 = 46 cm length of the rectangle.