11. Mark works two jobs to help pay for college. His job as a waiter pays him $9 per hour, x, and his job at the hotel pays
him $15 per hour, y. In a given week, Mark can work no more
than 20 hours a week due to his college commitments. Mark
wants to earn at least $180 a week, working a combination of
both jobs.

A. Write a system of inequalities that can be used to model the
situation.