The perimeter of the rectangle is 40 cm, its width is 6 cm. Find the area of the rectangle.

In order to find the area of a rectangle whose perimeter is 40 cm and width = 6 cm, it is necessary to find the unknown side.
Let’s express it from the perimeter formula:
P = 2a + 2b.
2a + 2 * 6 = 40.
We leave the variable with the coefficient on the left side of the equation, and transfer the number to the right, while the sign in front of it is changed to the opposite:
2a = 40 – 12 = 28.
To find the second factor, divide the product by the first:
a = 28: 2 = 14 cm – length.
The area corresponds to the formula:
S = a * b = 14 * 6 = 84 cm².