InfoPath Dev

I have two drop down fields data type time named TimeIn and TimeOut and another text box field named hours that I want to show the results of the time a user worked.

Example:

TimeIn = 9:00 AM TimeOut = 5:00 PM then hours = 8

I can't figure how in infopath to calculate the hours field, any ideas on how to solve this issue?

 

solved my issue with http://blogs.msdn.com/b/infopath/archive/2007/02/21/calculating-elapsed-time-without-code.aspx

(((substring-before(endTime, ":") * 60) + substring-before(substring-after(endTime, ":"), ":")) - ((substring-before(startTime, ":") * 60) + substring-before(substring-after(startTime, ":"), ":"))) / 60