Please help me with this question

Question

An automobile is approaching a train which is moving parallel to the road. What frequency is heard if the train sounds its whistle at a pitch of 212 Hz while it is traveling at a speed of 30.0 m/sec, if the automobile is also traveling at a speed of 25.0 m.sec? (Air temperature is 20.0°C).

My teacher gave me an answer of 249 Hz, and I don't know how did they get that answer

please help me

Answer 1

The car (speed is 25 m/sec) is approaching the train (speed is 30m/sec), so the frequency heard will be:

212 * (1+ 25/340) / (1-30/340) = 249.6 Hz