Question about doppler effect:

Question

How do you solve when it gives you percentage value? (Q 1) How do you calculate for doppler effect when the listener is moving instead of the source of sound? (Q 2)

Questions
1. As a racing car zooms by you, its pitch decreases by 20%. If the speed of sound is 345 m/s, how fast is the car travelling?

2. Find the apparent frequency of a person moving at 30 m/s hears if she is moving a) toward a stationary siren with frequency 1800 Hz. b) away from a stationary siren with a frequency 1800Hz