imc

The median of the list is $10$, and there are $9$ numbers in the list, so the median must be the 5th number from the left, which is $n+6$. We substitute the median for $10$ and the equation becomes $n+6=10$. Subtract both sides by 6 and we get $n=4$. $n+n+3+n+4+n+5+n+6+n+8+n+10+n+12+n+15=9n+63$. The mean of those numbers is $\frac{9n+63}{9}$ which is $n+7$. Substitute $n$ for $4$ and $4+7=\boxed{11}$.