The perimeter of triangle ABC is 21 cm. Side AB is 2 times smaller than side CB

The perimeter of triangle ABC is 21 cm. Side AB is 2 times smaller than side CB, and side CB is 4 cm larger than side AC. Find the sides of the triangle.

This problem is simple, but in order to solve it and get the correct answer, you will need to draw up a simple equation.
But first, we need to draw up a short condition for this task:
P – 21 centimeters;
AB -? centimeters;
СB -?, 2 times more than АС;
AC -?, 4 less than CB;
Let x cm – AB, then CB – 2x cm, and AC – 2x – 4 cm.Since the perimeter is 21 cm, we have the equation:
x + 2x + 2x – 4 = 25;
5x = 25;
x = 5 centimeters – AB;
5 * 2 = 10 centimeters – CB;
10 – 4 = 6 centimeters – AC;
Answer: 5, 10 and 6 centimeters.