43 and 5/6 because 12 and 1/4*2 is 24 and 1/2 then 9 and 2/3*2 is 19 and 1/3 and when you add that you get 43 and 5/6

Please consult the "Calculations" section of this ans .

The information we're given is below :
- slope : -1/3
- Point crossed by the line : (3, 6)
As per given information , we can do the following :
- Write the line's equation in point slope form
Point - slope form looks like so :
y-y₁=m(x-x₁)
y-6=-1/3(x-3)
y-6=-1/3x+1
y=-1/3x+1+7
y=-1/3x+6
↑ 

For every 9 kids 5 are girls
there are 3 sets of 9
so 5 x 3 = 15
there are 15 girls