A tire shop counted 80 invoices at the end of the month. They charge $325 for a set of new tires and $50 for a set of used tires. The total dollar amount of the invoices was $6,750. Let x represent the number of sets of new tires and y represent the number of sets of used tires. Which system of equations represents the situation? Select the correct answer below: O O O O x+y = 80 325x == 50y+ 6,750 x+y == 80 325x = -50y+6,750 x+y = 80 325x = -50y-6,750 x y 325x x+y 325x = 80 = -50y+6,750 = 80 -50v+6.750