Twelve teachers: t1, t2, ..., t12 have large groups, so you can only teach in the following rooms: A, B, C and D. The teachers have already been assigned their schedule, but the management does not yet know if it is possible to assign them one of the 4 large rooms in the schedule that was assigned to them. The assigned hours are as follows: t: 9am-10am t2: 11am-1pm t3: 10am-11am t4: 11am-12pm t5: 9am-11am t: 12 pm-1pm t7: 10 am-12pm tg: 9 am-10am tg: 11 am-12pm 10: 12pm-1pm t11: 10am-11am t12: 11am-12pm Is it possible to accommodate the 12 teachers and their groups in their respective schedules in one of the 4 large rooms? If not, would it be possible to change the schedule to just one teacher (to another with the same number of hours) between 9am and 1pm?