Center and Spread · Superchallenge problem

A school has two classes. Class A has $5$ boys with mean test score $60$ and $20$ girls with mean score $70$. Class B has $30$ boys with mean score $80$ and $n$ girls with mean score $90$. So in each class the girls average $10$ points more than the boys. What is the largest whole number $n$ for which the boys' mean over both classes is still higher than the girls' mean over both classes?