Answer:
There are 15 boys in the choir
Explanation:
If there are 45 girls in the choir and the ratio of boys to girl is 3 to 9, you would have to multiply the 9 by 5 to get 45. You have to do the same thing to both sides so you would also multiply the 3 by 5 to get 15. The new ratio is 15 to 45.
Hope this helps!