There are

ways of pairing up any 2 members from the pool of
contestants. Note that

so that

Answer:
the answer to the question is y=x+2.
Just so you know, you have to know at least one of the variables to find out what the other is. Like for example, X could equal 2, so that would make y equal 5. Or X could equal 23, and that would make y equal 26.
(5x+15)(6x-10)
= 30x^2 + 30x - 50x - 150
= 30x^2 - 20x - 150