In Access, in query design, go to View | SQL View
. Use the following function to get what you need:
DateDiff('d', [date case received], [transaction date])
This function will return the difference between the two dates, in the given increment (d=days). You can search Access help if you want a more thorough explanation.
So your ending SQL statement may look something like the following:
SELECT CaseId, [transaction date], [date case received], DateDiff('d', [date case received], [transaction date]) AS [Case Duration]
Note: You would not need to include [transaction date] and [date case received] in the return fields, I just included them for reference.
Let me know if this helps,