i think boys =18
girls=12
boys :x
girls:y
student:z
the number of group for the boys :n
the numberof group for the girls :m
so x=(3/5)z
y=(2/5) z
x/y=3/2
3y-2x=0
(1/10)zn=(3/5) z
so n=6
(1/5)zm=(2/5) z
put x=(1/10)z6
y=(1/5)z2
into 3y-2x=0 and z=30
z=30 so x=(1/10)306=18
y=(1/5)302=12