6. Flash Fasttrack (associate dean of janitorial services at Wombat University) must schedule the regular maintenance by his janitorial engineers. There are two crews: sweeping crew and waxing crew. Union rules prohibit sweepers from waxing and waxers from sweeping. A building’s floors must first be swept before they can be waxed. Flash must schedule the order in which maintenance crews will visit each of Wombat U’s six buildings. He wished to minimize the sequence’s total completion time. Times required to sweep and wax each building are as follows:

Sweeping Time Waxing Time Building (Hours) (Hours)

Astronomy 18 10 Biology 8 9 Chemistry 26 13 Drama 15 16 English 17 20 Foreign language 12 17

a. Schedule the crews through the buildings.

b. When will the waxing crew start and stop work in the chemistry building?

c. During the schedule, for how much time are sweepers and waxers available for other activities?