The length of one side is 12 cm, and its perimeter is 56 cm. Find the area of this rectangle.

It is known from the condition that the length of one side of the rectangle is 12 cm, and its perimeter is 56 cm. In order to find the area of this rectangle, we must find the length of the second side of the rectangle.
Let’s compose and solve an equation using the formula to find the perimeter of a rectangle.
P = 2 (a + b);
Let’s denote by x cm the length of the unknown side.
2 (12 + x) = 56;
12 + x = 56: 2;
12 + x = 28;
x = 28 – 12;
x = 16 cm the length of the second side of the rectangle.
We are looking for an area using the formula:
S = a * b = 12 * 16 = 192 cm2.