A police car's radar gun emits microwaves with a frequency of f1 = 7.50 GHz. The beam

Question:

A police car's radar gun emits microwaves with a frequency of f1 = 7.50 GHz. The beam reflects from a speeding car, which is moving toward the police car at 48.0 m/s with respect to the police car. The speeder's radar detector detects the microwave at a frequency f2.
(a) Which is larger, f1 or f2?
(b) Find the frequency difference f2 − f1.