Bob needs to reserve virtual machines on a cloud computing service to solve a number of problems before a deadline. He has two options: reserve some number of virtual machines that can each solve 12 problems before the deadline, or reserve some number of virtual machines that can each solve 15 problems before the deadline: with virtual machines that can each solve 12 problems, Bob will end up using all the virtual machines to their full capacity except one, which will have only 3 problems to solve; with virtual machines that can each solve 15 problems, Bob will end up using all the virtual machines to their full capacity except one, which will have only 9 problems to solve. Assuming that Bob has at most 60 problems to solve, how many problems does Bob have? O O