Please tell me how to solve below related rates problem

A police car is heading due north approaching an intersection at 45 miles per hour. It sees a car speed past on the cross street heading due east. The policemen pulls out his radar gun and measures the car to be moving away at 20miles par hour. if the police car and speeding car were both 0.5miles from the intersection at that time, how fast was the speeding car actually traveling?

(Answer : miles per hour)