How do you calculate elapsed time in hours between times on different dates?

For example, what is the number of hours between 9:00 AM on February 2, 2013 and 1 AM on February 9, 2013?
I made some guesses, used formulas from drop-down menus, used MS Office help, Googled "Excel How calculate elapsed time in hours between times on different dates" with no luck.
Joined this forum so I can express the question in words and get interactive help.
Introduced myself in the appropriate sub-forum first.
Thanks in advance.
Bob P.

Thanks,FDibbins. Your answer was close enough that I was able to adjust and get it to work. Had to change dates to this format:
A1....2/2/13 9:00
A2....2/9/13 1:00

Then A3....=(A2-A1)*24 was correct. Tested it with a couple of different dates/times and it seems robust.

Looking for the "solved" button.

Thanks!
Bob P.

There it was, but I had to log in again. I had logged out, then followed the link back to the thread in the notificaton email without logging in.
Cheers,
Bob P.