How would i go about solving 12,15,18

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?

Write the equation of the circle centered at (10,-2) with radius 2.

If f(x)=3 over x+2 - square root x-3 then f(7)=