Why am I getting the wrong speed for a train using the Doppler effect formula?

[san512]

Homework Statement

A train moving at a constant speed is passing a stationary observer on a platform. A flute player is playing a note with a frequency of 940Hz. after the flute has passed, the observer hears the sound frequency of 915Hz. What is the speed of the train? The speed of sound in air is 343m/s.

Homework Equations

Fo = Fs (1/(1+(Vs/V))

The Attempt at a Solution

Vs = ((Fs/Fo) - 1) * V

When i input the given information I keep getting the wrong answer. Is my arithmetic wrong or am I missing something completely?

 

[Mickey Tee]

What is the given answer and what are you getting?

 

[san512]

A) 7.3 m/s
B) 12 m/s
C) 21 m/s
D) 32 m/s
E) 42 m/s

I get 9.4 m/s

 

[Mickey Tee]

Same here unfortunately.