This question need to be done in cplex configuration, it requires a model and a data. The answer should be codes in cplex, model and data. IBM ILOG CPLEX Optimization Studio Version 12.8

Greydog Bus Company operates buses between Boston and Washington DC. A bus trip between these two cities takes 6 hours. Federal law requires that a driver rest for four or more hours between trips. A drivers workday consists of a full round trip: one from Boston to Washington and one from Washington to Boston. The table below gives the departure times for the buses. Greydogs goal is to minimise the total downtime for all drivers. How should Greyhound assign drivers to round trips? Note, it is possible for a drivers day to overlap midnight. For example, a Washington-based driver could be assigned to the Washington-Boston 3PM trip and the Boston-Washington 6AM trip.

Trip	Departure Time	Trip	Departure Time
Boston 1	6:00 AM	Washington 1	5:30 AM
Boston 2	7:30 AM	Washington 2	7:30 AM
Boston 3	8:00 AM	Washington 3	9:00 AM
Boston 4	9:30 AM	Washington 4	11:30 AM
Boston 5	11:30 AM	Washington 5	1:00 PM
Boston 6	2:30 PM	Washington 6	3:00 PM
Boston 7	6:00 PM	Washington 7	5:00 PM
Boston 8	7:00 PM	Washington 8	6:30 PM
Boston 9	9:30 PM	Washington 9	10:00 PM
Boston 10	12:30 AM	Washington 10	12:00 AM (midnight)