A group of students go apple-picking. On average, each boy picks $30$ apples and each girl picks $20$ apples. The average number of apples picked by everyone in this groups is $26$. If there are $15$ boys, then how many girls are there in the group? 
选项为:A:$$15$$  B:$$10$$  C:$$9$$  D:$$20$$  E:$$23$$  请回答其中一个选项.