The side of the rectangle is 12 cm and the perimeter is 40 find the other side of the rectangle.

We are given a rectangle with a length of one of the sides – 12 cm.And the rectangle is also known and it is equal to 40 cm.
And we need to find the length of the second side. To find the length of the second side, compose and solve a linear equation.
So, let’s denote by x cm the length of the second side of the rectangle. To calculate the perimeter of a rectangle, use the formula:
P = 2 (a + b);
We substitute all the values in the formula:
2 (12 + x) = 40;
We solve the equation:
12 + x = 20;
x = 20 – 12;
x = 8 cm second side length.
Answer: 8 cm.