## Primitive Recursive

Hi

I am really stuck on the following question. Perhaps I am missing something really obvious here.

Show that $R(n,m)\longleftrightarrow max(10n,15m) \leq 3000$ is primitive recursive

I started by getting to

$max(10n,15m)=10n+15m- min(10n,15m)$

Is this right? If so I don't know where to go with it.