Thanks for the help! I understand your solution but I don't really understand why is it so.

The given info is that a class has 4 freshman boys, 6 freshman girls and 6 sophomore boys.

Therefore even if sophomore girls aren't even mentioned in the question, we can actually find the answer, like you've done. I'm not quite understanding the question because aren't there supposed to be only 16 students in class?

If the answer is 9 sophomore girls, aren't there more than 16 students in class? Is it because I don't see the question containing 'there are n numbers of sophomore girls in class', that's why I'm having problems seeing the way to do it?