Subset of Urns

Fix positive integers $n,k,$ and $r$ with $1 \leq r \leq \min(n,k)$. There are $n$ distinct urns before you. You want to arrange $k$ identical balls into these $n$ urns such that exactly $r$ of them are non-empty. How many ways can this done if $n = 10, r = 5,$ and $k = 8$?