Solve the all parts of given question:

Question: To study the Doppler shift on your own, you take an electronic tone generating device that is set to a frequency of 720 Hz to a campus wishing well known as "The Abyss." When you hold the device at arm's length (1.00 m), you measure its intensity level to be 80.0 dB. You then drop the tuner down the hole, listening to its sound as it falls.

Part A: After the tuner has fallen for 5.50 s, what frequency do you hear?

Part B: Estimate the time at which you can no longer hear the tuner.

Please give me an explanation for above question.