Question

Half of the students in Max's class volunteer at the local community center.Fifteen students do not volunteer.If there are 12 boys in Max's class, how many girls are in the class? Write and solve an equation.

Answer 1

Because half of the students volunteered and 15 didn't, there are 30 students. Now take that subtract by 12 and you get the number of girls. 
Equation: 15(2)-12=y
y=18

Answer 2

The answer is 18. the equation is (15 x 2) - 12. hope I helped :)