Explain why 2.15 and -2.15 are opposite

Someone answer asap for ! the total ticket sales for a high school basketball game were $2,260. the ticket price for students were $2.25 less than the adult ticket price. the number of adult tickets sold was 230, and the number of student tickets sold was 180. what was the price of an adult ticket?

With alll of except for the 2 that i did already

Benefit(s) from large economies of scale, in which the costs of goods decrease as output increases. natural monopolles perfect competition