A train which is traveling at 80 mi/h applies its brakes as it reaches point A and slows down with a constant deceleration. Its decreased velocity is observed to be 60 mi/h as it passes a point 1/2 mi beyond A. A car moving at 50 mi/h passes point B at the same instant that the train reaches point A. In an unwise effort to beat the train to the crossing, the driver “steps on the gas.” Calculate the constant acceleration a that the car must have in order to beat the train to the crossing by 4 seconds and find the velocity v of the car as it reaches the crossing.