A group has chartered a bus to New York City. The driver costs $100, the bus costs

Question:

A group has chartered a bus to New York City. The driver costs $100, the bus costs $500, and tolls will cost $75. The driver’s fee is nonrefundable, but the bus may be canceled a week in advance at a charge of only $50. At $18 per ticket, how many people must buy tickets so that the trip need not be canceled?