1. The problem statement, all variables and given/known data Two trains emit whistles of the same frequency, 282 Hz. If one train is at rest and the other is traveling at 45 km/h away from an observer at rest, what beat frequency will the observer detect? 2. Relevant equations 3. The attempt at a solution I used listener behind formula and got an answer of 544 Hz because i doubled the Frequency source. The answer is wrong, please help me!Thanks!