If you are looking for a 6 pack, you have to understand that a 6 pack is made in the kitchen. A 6 pack shows that you have a low body fat percentage more than ab strength. As far as push ups go, you should do approximately all of them. Seriously though, just go until you can't do any more.
I m 15, start with doing at least 50 push ups a day then 50 wide arm push ups and 25, diamond push ups do 100 Crunches a day 100 left and right oblique crunches and 100 diamond crunches to start off and add more and more each time abd change up the excesises each week