I’m not for sure that this is the answer but I tried. I’m pretty sure that it would be 10 boys on each team.
Explanation:
Since there are less boys than girls the teams must be even so if you put 10 boys and 10 girls on each team which there would only be 2 teams. 20 boys would be playing and 15 would be sitting out. 20 girls would be playing 5 would be out. Hope this sorta helped even though I’m not 100% sure this is correct