The professor from problem 6 is considering reducing the time for completion of the project. He can hire a teaching assistant (TA) to help with the new course, but this will cost additional money. The TA can help reduce the times only for activities A, D, and C. In each case the TA can reduce the time required by one day for $150 and two days for $300. Which activity should the TA perform to reduce the project completion time by one day?