A train accelerates uniformly from rest at a station A to a maximum speed of 80km/h and then maintains this speed for a certain time. It then decelerates uniformly to come to a stop at station B, 60km from A. The time taken from A to B is 1 hour. If the rate of acceleration is half the rate of deceleration, find (a) the acceleration in m/s, and (b) the time during which the constant speed was maintained.​