Write and solve a system of inequalities to model the following situation. The local waterpark is opening for the summer. They are selling adult tickets for $15 and child tickets for $8. The park can hold at most 500 people. To allow access for more children, the waterpark is limiting the number of adults to no more than 150. The waterpark is hoping to make at least $600 in ticket sales. How many adult tickets and how many child tickets should be sold to maximize the amount of money earned?