Physics help?

a car and a coach travel at different uniform speeds on a straight horizontal road.the speeds of the car and the coach are 12ms^-1 abd 10ms^-1 respectively. while the car lags behind the coach by 20m, the car accelerates uniformly at 0.5ms^-2 and the coach keeps travelling at a constant speed.how long would it be for the car to overtake the coach?