What you do, is you add the ratio 7:5, so 7+5, which makes 12. Then, you must do 36 divided by 12 to give you one part, which is 3. You do 3 multiplied by 7, which gives you 21 boys and 3 multiplied by 5 gives you 15 girls. Then, to find the difference, you do 21-15 which gives you the difference of 6. Your final answer will be six! I hope this helped. :D
