Let us denote the number of boys in the glee club with X and the number of girls with Y.
There are 84 students in the glee club, which means that the following equation can be written:
X+Y=84
We also now that there are 12 more boys than girls, so:
X=Y+12
We can rewrite the first equation like:
(Y+12)+Y=84
2Y+12=84
2Y=62
Y=62/2=31
X=31+12=43
So, the ratio of the number of girls to the number of boys is: Y/X=31/43