How fast should the bat fly, vb, to hear a beat frequency of 195Hz?

A bat flies toward a wall, emitting a steady sound with a frequency of 22.0 \rm{kHz}. This bat hears its own sound plus the sound reflected by the wall.How fast should the bat fly, vb, to hear a beat frequency of 195Hz?
Doppler frequency shift percent= 195/22000 = 0.00886



So the bat must fly (.00886 th) the speed of sound towards the wall



==%26gt; if sound travels at 330 m/s then the bat must fly



(.00886)(330m/s) = 2.938 m/sec to get that 195 Hz beat frequency