The length of the rectangle is 2 times longer or 15 cm longer than the width. Find the perimeter (in cm) of the rectangle.

Let the width of the rectangle be x, then, by the problem statement, the length of the rectangle is 2x or (x + 15).
We find the perimeter of the rectangle by the formula:
P = (a + b) * 2.
Let’s compose and solve the equation.
(x + 2x) * 2 = (x + x +15) * 2
6x = 4x + 30
2x = 30
x = 15 (cm) – the width of the rectangle.
15 + 15 = 30 (cm) or 2 * 15 = 30 (cm) – the length of the rectangle.
(15 + 30) * 2 = 90 (cm) – the perimeter of the rectangle.
Answer: 90 cm.