Question

lance bought 3 cd's and spent 27$. Jacob bought 5 cd's and spent 45$. Is this a direct variation?

Answer 1

direct variation means you can find a positive number (call it k) where
cost = k * number of cd's

Answer 2

what about y=x-13

Answer 3

not relevant here. The question is asking is there direct variation, which is just a way to ask does
cost= k*CD's

the reason this is useful, is if you know k, you can figure the cost for any number of cd's

the way to do this is divide:
cost/CD = k
if you get the same number for both guys, then you have direct variation