Suppose that a police car is moving to the right at 26.1 m/s, while a speeder is coming up from behind at a speed of 39.4 m/s, both speeds being with respect to the ground. Assume that the electromagnetic wave emitted by the radar gun has a frequency of 7.83*109 Hz. Calculate the magnitude of the difference between the frequency of the emitted wave and the wave that returns to the police car after reflecting from the speeder's car.