Speed distance time I'm sure.

I'm sure it is easy but I just cant get my head around it...

Police car chasing an offender. At point A police car is travelling 90mph and offender is 300 meters ahead. At point B offender is 800 meters ahead.

Distance between A and B is 0.6 Miles.

Speed of police vehicle is constant, 90mph.

What is the minimum speed of the offender to increase the gap by 500 meters?

Answers on a post card (Happy)

Find the time T it takes for the police car to go from A to B. During this time, the excess of the offender's speed over the police speed was responsible for increasing the gap by 500 meters. In other words, you may assume that the police car was stationary and the offender's car, moving at speed , covered 500 meters in time T.