Excel Date Manipulation Function

Excel Date Manipulation Function

I have an excel table that contains start times and end times and the
added hours. Here is what it looks like
***********************************
* Start Time ** End Time ** Hours *
***********************************
***********************************
* 8:00 AM ** 3:30 PM ** 7:30 *
***********************************
* 7:30 AM ** 4:00 PM ** 8:30 *
***********************************
The Hours column contains this function:
=TEXT(C3-B3,"h:mm")
I need a function that can add up the hours column to find total hours.
Every function I have tried has not worked. Thanks in advance!