The perimeter of the rectangle is 48 cm one side 15 which is the second side.

The perimeter of a rectangle is equal to the sum of the lengths of all its sides. Since the opposite sides of the rectangle are equal, then P = 2 * a + 2 * b. Substituting the known values of the perimeter and one of the sides, we can find the second side: 48 = 2 * 15 + 2 * b, 48 = 30 + 2 * b, 2 * b = 48 -30, 2 * b = 18, b = 18 / 2, h = 9 cm.
Answer: The second side of the rectangle is 9 cm.