Shelia's car is stopped at a traffic light. She is sitting in the car, waiting for the light to turn green. Suddenly, from behind her, Shelia hears a police car approaching, blowing it's siren. The frequency of the siren sound she hears is 8.5 hz, and as soon as the car passes her by, the frequency of the siren sound she hears becomes 75 hz. Knowing that sound travels through air with the speed of 340 m/s, find the following:
A) the speed of the police car
B) the frequency of the police siren