Enter parimeter value question

[SFC]

I have a report that has two textboxes and thier data control source is are values from a table (say, Qty & Price).
I have another textbox (Extension) that the data source multiplies two of the textboxes mentioned above (Qty & Price).


In my report footer I have another textbox (textboxname) that will sum the textbox (Extension).
My problem is that when I run the report I get a dialog box asking me for the parameter of the textbox that I want to produce a sum in the footer.
Why doesn't it just sum the textbox? The expression in the texbox is =Sum([texboxname])

Thanks,
Steve

[June7]

Header/footer calcs can't refer to controls, must refer to fields. Either do the Qty * Price calc in query and refer to the constructed field or do footer calc like: =Sum(Qty * Price)

[SFC]

Thank you for your input, I'll give it a try.