Since most of Microsoft Office Suites do not have SetField action, I have used a different and easier approach.

I have used the opened the Contract Form in datasheet view then used SetProperty action to calculate.

The [RentalDate] + [NoOfDays] has been calculated by the SetProperty. 

The reason why I have used the OpenForm action before claculating is because:
	The SetProperty  action cannot be executed without opening a Form or Report.

Hope you will understand this. :-)
