Frequency Problem, need urgent help please 1. The problem statement, all variables and given/known data A train moving west at a speed of 30 m/s emits a whistle at a frequency of 348 Hz. On another train behind the first train and moving west at a speed of 20 m/s, the engineer hears the whistle from the first train. If the speed of sound in air is 343 m/s what is the frequency of the sound heard by the second train engineer? 2. Relevant equations (I believe this is it) f' = (1/1+- u/v)f 3. The attempt at a solution To be honest I've tried my best to figure this out but I'm simply lost on it. Thanks.