How do you write this equation "at a concert, you purchase 3 t-shirts and a concert program for a total cost of $90.the program cost $15 and the t-shirts all cost the same. write and solve an equation to find the cost of one t-shirt."

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.