As a school bus driver, Charlie takes pride in safely taking the neighborhood children to school every day. At the beginning of this school year, Charlie was excited when he was given a much newer bus to drive his route. Charlie's bus has 30 miles on it after 1 school day. His bus has 50 miles on it after 3 school days. In this relationship, x represents the number of school days Charlie has been driving his new bus, and y represents the total number of miles the bus has been driven.