PLEASE HELP- How much to offer on a note?

Hi,

I have someone who is going through foreclosure. The property is over encumbered to sell it. So, I want to tie up the property and buy it only if I can make it a win-win situation for theseller and I by buying the notes.

The first loan is for 160k and the second is 40k. Does the same rule apply for offering to buy a note as it does for a short sale? For example, 80% on first and 7-10% on second?

Thanks in Advance