A Woman Is Riding a Bicycle at 18

Short Answer

A woman is riding a bicycle at 18.0 m/s along a straight road that runs parallel to and right next to some railroad tracks.She hears the whistle of a train that is behind.The frequency emitted by the train is 840 Hz,but the frequency the woman hears is 778 Hz.Take the speed of sound to be 340 m/s.
(a)What is the speed of the train,and is the train traveling away from or toward the bicycle?
(b)What frequency is heard by a stationary observer located between the train and the bicycle?