Need expression help ASAP

I have a report in ssrs where it has a colum with dates in it I has and other colum with either a $0.00 amount or and amount paid. I need a colum which which calculates only the number of days from the date colum that when the other colum =0 it gives me the total number of days. VS.net SQL 2005 SSRS C#

example of what needed:

Invoice amount | Date of Invoice| Amount received | number days past due

$100.00 06/01/2007 0.00 18 days ( this is what I need)

can some one explain.

Here are my expressions

FormatCurrency(Fields!Grossamtbilled.value)

FormatDateTime(Fields!EXPR1.Value,2)

FormatCurrency(Fields!RCVAMOUNT.Value)

I'm not sure what expression you would use when creating a report, but it would be fairly easy to do it in the original SQL Statement (by using a mixture of the CASE and DateDiff functions).

sql