MATH! a prospective seller doesn't know what she owes

[Kim Handelman]

Hi, I got a call today on a house. The woman paid $79,000 for it in 2006. She knows she over paid and doesn't think she can sell it without being able to pay off her loan which would mean a short sale. She doesn't know how much she owes and can't find a statement (in total denial). I'd like to do some basic math on the classic loan of that time to see if it's even worth digging deeper on this property. So Assuming she put 20% down, at 6.5% (average for that year), how much would she owe? I don't know how to calculate an amortized loan pay down since the interest amount changes every month because the principal gets paid down every month. There's got to be a formula right? -k-