There are probably more elegant methods but this will do the trick.

First of all, Excel doesn't think of those numbers as "times" even
though the "look" like times. The are actually fractions of a day.
Try formatting your 9:00 as a number and you'll see .375 which means
that by 9:00 am .375 of the day has gone by. If I use the formula
sum(C4,C5,C6) I get either 23:30 or .98 depending on how the cell is
formated (time or number). Remember, the actual value is .98 but it
may be formatted to "look" like time.

To convert the .98 of a day to hours, simply multiply it by 24 hours
and remember to format it as a number.

=sum(C4:C6) * 24 should do the trick.

- John
www.johnmichl.com