Waves and Sounds - speed of a bat

[FrenchAtticus]

Homework Statement

A bat moving at 4.5 m/s is chasing a flying insect insect. The bat emits a 52 kHz chirp and receives back an echo at 52.75 kHz. At what speed is the bat gaining on its prey? Take the speed of sound in air to be 342 m/s.

Homework Equations

f1 = f ((velocity +/- velocity observer)/(velocity +/- velocity source))

The Attempt at a Solution

To start off, I converted 52 kHz to 52,000 Hz and 52.75 kHz

Then my equation looked like:

52750 = 52000 ((342 - vo)/(342-4.5)

I found vo to be .367788 and subtracted that from 4.5 to find the speed gained, but that doesn't seem to work. Can anyone help?

 

[FrenchAtticus]

Can anybody help me out?