How do you put the Num-Days and Hours into total hours

on Excel, I have 2 fields.
one (number format cell) has the number of days.
another (time format cell) has hh:mm is there a way to make another
cell to have days/hours?

OR, if you would rather.

12/17/2008 13:23
12/19/2008 15:35
given these "date and time" fields, is there a way to derive the total
number of hours between the two?

Thanks,
Crzzy1