Answer:
There are 45 boys.
Explanation:
The best way to easily solvethis is by making equations, see below.


Now we can subtract the secons equation from the first.

I'm also goong to multiply the equatipn by 5 to remove the fraction.

Now simplify

Now we found out there are 75 girls. Now we insert this into our second equation to find how many boys there are.

Now we know there are 45 boys.