Luis, Carlo, and Ken bought movie tickets. Each ticket cost the same
amount. The 3 tickets cost $21. How
much did Carlo pay for his ticket?
Use a model to justify your answer.

Three students, javier, sam, and corrine, participated in a fundraiser where people donated a certain amount of money per lap that the student ran. each student also had some initial donations that were collected before the run. the equations that represent each student's total donation, y, based on the number of laps ran, x, is shown below. match each equation with the correct rate of change for that student.