Find the lengths of the sides of the rectangle if the perimeter is 36 dm and the width is the second part of the length.

Perimeter – 36 dm;
The first side is? dm;
The second side is? dm, the second part of the first;
Let’s compose an equation based on the formula for the perimeter of a rectangle:
Let x dm be the second side, then 2x dm is the first side. Since it is known that the perimeter of the rectangle is 36 dm, we have the equation:
36 = 2 * (x + 2x);
Divide both sides of the equation by two, and also perform the action inside the brackets:
18 = 3x;
x = 18: 3;
x = 6 dm – the second side;
6 * 2 = 12 dm – the first side;
Answer: 6 dm and 12 dm.