求助 官版12th 综合14题如何做

GMATHK2012

Of the 84 parents who attended a meeting at a school 35 volunteered to supervise children during the shchool picnic and 11 volunteered both to superviese children druing the picnic and to bring refreshements to the picnic, if the number of parents who volunteered to bring refreshements was 1.5 times the number of parents who neither volunteered to bring refreshments, how many of the parents  volunteered to bring refreshements

答案是
25
36
38
42
45
请先翻译下然后给出答案，谢谢啦