There are 12 third grade students and 15 fourth grade students in the band. They will travel to a convert in cars that can hold 4 students each. Which of these can be used to find out how many cars are needed to drive the students?
(12 + 15) ÷ 4 = s
(15 - 12) ÷ 4 = s
15 + 12 - 4 = s
15 + 12 + 4 = s