Calculating Time Passed

Calculating Time Passed

Hi,

I collect two fields - a date field and time field.  I have a workflow to load a previous record and loading the previous dates into the current record.  How could I combine the two and determine the time passed between them?

Current Date:
Current Time:
Previous Date:
Previous Time:

Ideally, I would like to do break it down into hours:minutes.

Thank You
Chris