Situation 15.1 A Train Is Approaching a Signal Tower at a Speed

Situation 15.1
A train is approaching a signal tower at a speed of 40 m/s.The train engineer sounds the 1000 Hz whistle and a switchman in the tower responds by sounding the 1200 Hz siren.The air is still and the speed of sound is 340 m/s.
-In Situation 15.1,the frequency of the train whistle tone,heard by the switchman,in SI units,is given by:

A) 1000
B) 300/340 × 1000
C) 340/300 × 1000
D) 340/380 × 1000
E) 380/340 × 1000