how do you work with time?

From: Annelie (lkelady33_at_yahoo.com)
Date: 05/29/04 

Date: Sat, 29 May 2004 18:18:25 -0400

I am trying to create input for a time card
Start: 07:44 (shorttime format)
End: 17:13 (shorttime format)
HoursWorked: 09:29 (shorttime format)- formula was =[end]-[start]

Now how do I work with my HoursWorked
I need to work with the hours
I tried Int([hoursworked])
it give me an error
Everything I have tried gives me an error
Help
Annelie