B. 12
Ex: 12 squared is 144
84 to 62. You have to subtract 146-84 to get the number of girls from the class.
This question is asking you for the least common multiple of 60 (seconds in 1 minute) and 24 (seconds in 24 seconds).
I think it's 120 (you should check it) and that would be 3 minutes.
