As You Stand by the Side of the Road, a Car

Multiple Choice

As you stand by the side of the road, a car approaches you at a constant speed, sounding its horn, and you hear a frequency of 80.0 Hz. After the car goes by, you hear a frequency of 60.0 Hz. What is the speed of the car? Assume that he speed of sound in air is 343 m/s.

A) 64 m/s
B) 49 m/s
C) 16 m/s
D) 36 m/s
E) 25 m/s