The perimeter of the rectangle is 34cm and one of its sides is 12cm. Find the length of the second side of the rectangle.

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 34 centimeters, and one of the sides is 12 cm, we calculate the length of the second side.
2 * (a + 12) = 34;
a + 12 = 34/2;
a + 12 = 17;
a = 17 – 12;
a = 5 cm.
Answer: 5 centimeters.