i'm not sure what you're trying to ask but,
in 1 week, y will have 6 cards. 6=4(1)+2
in 2 weeks, y will have 10 cards. 10=4(2)+2
in 3 weeks, y will have 14 cards. 14=4(3)+2
you basically just substitute in the number of weeks with x and then just solve the problem to find out the total number of cards