Answer:
frequency when car is approaching comes out to be 821 Hz
car is moving away from the object comes out to be 780 Hz
Step-by-step explanation:
car speed = 20 mph = 8.94 m/s
speed of sound = 343 m/s
violin frequency = 800 Hz
when car is approaching:

when car is moving away

hence the frequency when car is approaching comes out to be 821 Hz
and when the car is moving away from the object comes out to be 780 Hz