Poof out of existence

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?

Typically a point in a three dimensional cartesian coordinate system is represented by which of the following answers in the picture !

Asequence is a function whose is the set of natural numbers