A commuter train passes a passenger platform at a constant speed of 39.9 m/s. The train horn is sounded at its characteristic frequency of 320 Hertz.
(a) Find what overall change in frequency is detected by a person on the platform as the train moves from approaching to receding? (Indicate whether the frequency increases or decreases with the sign of your answer.)
___________Hz
(b) Find what wavelength is detected by a person on the platform as the train approaches?
___________m