Please Help :
 Last Year three 6th grade students , Aliya, Crystal, And Shamika, we’re selling balloons at the schools Winter Dance to collect $305 for a class trip to the Zoo. Aliya sold 2 more balloons than Crystal, And Shamika sold twice as much balloons as Crystal. Let “C” represent the total number of balloons Crystal Sold. 
Total Ballons Sold : 122
F) Which number in the following set represents the amount of balloons sold by Crystal? 
 { 30, 31, 116, 118 }
Thanks