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