Keke, this is the solution:
f (x) = 50 (0.6) ^x
Height of the first bounce = 50 (0.6)
Height of the first bounce = 30 feet
Height of the second bounce = 50 (0.6)²
Height of the second bounce = 50 * 0.36
Height of the second bounce = 18 feet
Height of the third bounce = 50 (0.6) ^3
Height of the third bounce = 50 * 0.216
Height of the third bounce = 10.8 feet