Monica wants to purchase at least 20 minutes of computer time from a time-sharing computer company. She needs at least 7 minutes from
Computer A. The time-sharing company will rent Computer A only if the user agrees
also to rent Computer B for at least 5 minutes. The rent for Computer A is $500 per
minute and the rent for Computer B is $200 per minute. In order to minimize the
total cost, how much computer time should Monica buy on each machine?