Question

Another question please.
At a school band concert, Christopher and Celine sell memberships for the band's booster club. An adult membership costs $10 and a student costs $5.
At the end of the evening, the students had sold 50 memberships for a total of $400. The club president wants know to know how many of them are adults and how many are students.
The question is,
1.What equation relates x and y to the $400 income?
(Let X be the number of $10 adult membership and Y for the student membership)