A train is moving parallel to a highway with a constant speed of 20.0 m/s. A car is traveling in the same direction as the train with a speed of 40.0 m/s. The car horn sounds at a frequency of 510 Hz, and the train whistle sounds at a frequency of 320 Hz.
(a) When the car is behind the train, what frequency does an occupant of the car observe for the train whistle?
(b) After the car passes and is in front of the train, what frequency does a train passenger observe for the car horn?