jmc

Converting into minutes and adding, we get that she skated $75\ast 5+90\ast 3+x=375+270+x=645+x$ minutes total, where $x$ is the amount she skated on day $9$. Dividing by $9$ to get the average, we get $\frac{645+x}{9}=85$. Solving for $x$, $$645+x=765$$ $$x=120$$ Now we convert back into hours and minutes to get $\boxed{\text{2 hr}}$.