A commuter train traveling at 40 mi/ h is 3 mi from a station. The train then decelerates so that its speed is 20 mi/ h when it is 0.5 mi from the station. Knowing that the train arrives at the station 7.5 min after beginning to decelerate and assuming constant decelerations, determine ( a) the time required for the train to travel the first 2.5 mi, ( b) the speed of the train as it arrives at the station, ( c) the final constant deceleration of the train.