You Are Driving Along a Highway at 35

Multiple Choice

You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind at constant speed and you perceive the frequency as
.You are relieved that he is in pursuit of a different driver when he continues past you,but now you perceive the frequency as
What is the speed of the police car? The speed of sound in air is

A) 38.4 m/s
B) 30 m/s
C) 39.2 m/s
D) 40.1 m/s
E) 41.7 m/s