M equals

M-girls was elected, and it was full.

Diverse

The number of boys and one girl and the overall elected m-girls.

All the arrangements have been made. (This can't be marked here) In other words,

M=5×4×3×2+(2+X)！

N equals

Full platoon of girls

Diverse

Boys' platoon

Diverse

Men and women are arranged as a whole.

that is

N=

5! ×

x！ ×2

Because 5M=36N

Instead of calculating, get

X=7 .

The group size is 5+7= 12.