Reply to My remix on someone else's EP - Need help

So I made a remix for this kid, and it is going to be on his new EP. He is wanting to sell his EP for $10...my question is should I get a percentage of each sale? Also he is going to be selling my remix on his EP, but atm I want all of my tracks to be free. I'm really not worried about the money, I just want the chance to gain some followers.