While standing near a railroad crossing, a person hears a distant train horn. According to the train's engineer, the frequency emitted by the horn is 440 Hz. The train is traveling at 20.0 m/s and the speed of sound is 346 m/s. a) What would be the frequency of the train's horn if the train were at rest? b) What is the adjusted frequency that reaches the bystander as the train approaches the crossing? c) What is the adjusted frequency that reaches the bystander once the train has passed the crossing?