Crystal Reports Convert date format and append it with Time

Message

   Hi,

I have a requirement of this type. we have In date,In time,Out date,out time. we need to capture all these details and compare them and need to display the time diff.

eg:  In Date    5/15/2008 12:00:00 AM
       Out date  5/15/2008 12:00:00 AM
       In Time    5/15/2008 8:00:00 AM
       Out Time  5/15/2008 5:00:00 PM
My formulae should work such that 
I need to get Date from In Date and append it with In Time
eg: In DateTime   2008/15/05 08:00
      Out DateTime 2008/15/05 17:00
Here i need to compare these to fields and get the output. 
I need to get Time in in the In DateTime,Out DateTime and compare and display the Total time.

Can any one of you help me out in solving this.

Thank you,
Akki