I need step-by-step help with this physics problem?

A motorist traveling at a constant speed of 130 km/hr in a 50 km/hr zone pes a parked police car. Three seconds after the car pes, the Police car starts off in pursuit. The policeman accelerates at 2m/s^2 up to a speed of 50m/s and then continues at this speed until he overtakes the speeding motorist. How long from the time he started does it take the police car to overtake the motorist? the motorist continues at a constant speed during this process.