A Police Car Siren Emits a Sound at 600 Hz

Multiple Choice

A police car siren emits a sound at 600 Hz.If an observer moves toward the source at 50 km/hr,and the police car approaches the observer at 100 km/hr (all speeds relative to the road) ,calculate the siren frequency heard by the driver of the police car (assume the speed of sound in air = 343 m/s) .

A) 626 Hz
B) 600 Hz
C) 679 Hz
D) 577 Hz
E) 970 Hz