the answer is not 17500

Department A and Department B are each considering renting a copy machine for work needed during the month. Department A needs the machine 100 hours, and Department B needs the machine 400 hours. Normally, the machine rental is $50/hour. If A and B rent together, the hourly rate becomes $45/hour. Using the incremental cost method, and assuming that A is the primary user, how much of the cost is allocated to B? None of the choices is correct. 4,500 17,500 12,500 5,000 22,500