Question

I have a few questions that i am not too sure how to figure out...
1- as a racing car zooms by you, its pitch decreases by 20%. If the speed of sound is 345m/s, how fast is the car travelling?

2-a person has a threshold of hearing of 5db. another person has a threshold of hearing of 25db. Which person has better hearing and by how much?

PLEASE HELP! :(
1. Solve (a+V)/(a-V) = 0.8
a is the speed of sound, and V is the car's speed.

2. The person who can hear the lower 5 dB level has better hearing, by 20 dB. That is a factor of 100 times less in sound power level
I do not really know but somthing to do with isolating Vo ?

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