Solve the mathematical puzzle. determine the digits of r from these clues. the first digit is the answer when the third digit is divided by 2. the second and third digits add to 7. the second digit minus the first digit is 1. r is a three-digit number:

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?