The sum is of n and 14 can be written as:
n+14=72
Without speeding up it would take 5 1/3 seconds.. not sure if it speeds up in the question?
First hit it travels 48 ft
Second hit it travels 24 + 24 ft
third hit 12 + 12
4th hit 6 + 6 ft
Total = 48 + 48 + 24 + 12 = 132 ft Answer