The sum of the house sides of the rectangle is 56 cm. If its width is 4 cm, then the length is ….

To solve this problem, remember that the perimeter of a rectangle is the sum of the lengths of all its sides. Since in a rectangle the opposite sides are equal, then P = 2 * (a + b), where a is the length, b is the width. Knowing that the perimeter is 56 cm and the width is 4 cm, we calculate the length.
56 = 2 * (a + 4);
a + 4 = 56/2;
a + 4 = 28;
a = 28-4;
a = 24 cm;
Answer: 24 cm.