A student holds a tuning fork oscillating at 256 Hz. He walks toward a wall at a

Question:

A student holds a tuning fork oscillating at 256 Hz. He walks toward a wall at a constant speed of 1.33 m/s.
(a) What beat frequency does he observe between the tuning fork and its echo?
(b) How fast must he walk away from the wall to observe a beat frequency of 5.00 Hz?