Why does this thing say i have too many registrations ive never used this site and now i see why lol im trying to get one simple already asked answer and this site wont let me wow why did i even try

Sophia wrote an equation to represent the revenue of a movie theater for one day. she let x represent the number of child tickets sold and y represents the nunver of adult tickets sold. if a child ticket cost $4, an adult ticket cost $6, and the total revenue for the daybwas $420, which equation could sophia use to represent the number of chikd and adult tickets that were sold?