Number Puzzle

Marston sent me this puzzle:

If:

2 + 3 = 10

7 + 2 = 63

6 + 5 = 66

8 + 4 = 96

Then:

9 + 7 = ?

The answer is the password to an attached spreadsheet. Figure out the answer, and you can open the spreadsheet and add your name to the list of people who have solved this problem. Only problem is I don't have Microsoft Excel. I do have Open Office, so I can open Excel spreadsheets, and when I try to open this one it does indeed check for a valid password. However, I cannot save it as a protected spreadsheet in any format, so I could not add my name to the list. Some deficiency in Open Office, I suppose. So now I am in a bind. I cannot demonstrate that I can solve the puzzle without giving you the solution. Of course by now this problem and its' solution are all over the net, so if you really wanted to cheat, you could. The problem is not that difficult, so if you enjoy this kind of thing, you might try to solve it. If you want, I can forward the protected spreadsheet to you so you can amuse your friends.

After I used Open Office to convert the spreadsheet to the Open Office format, I was able to upload it to Google Documents, but when I tried that with the protected Excel format version, I got an error.