Abat flies toward a wall, emitting a steady sound of frequency 1.70 khz. this bat hears its own sound plus the sound reflected by the wall.

I believe the question is missing this sentence: how fast should the bat fly in order to hear a beat frequency of 8.00 Hz? The solution would be like this for this specific problem:

8.00 / 1700 = 2 * v / 340m/s 
v = 0.8 m/s 

So, in order to hear a beat frequency of 8.00 Hz, the bat should fly 0.8m/s.

d) physical means can be used to separate the components of air.