In a report table there is this formula to calculate a subtotal for an invoice. This is the formula:
=Sum(Fields!LineTotal.Value)
The textb
Have you tried creating a report variable? Create a new variable and put the invoice calculation into the expression for the new variable. Then reference the report variable from the two textboxes.
The source for the two textboxes would look something like this:
=Variables!TestVariable.Value
http://msdn.microsoft.com/en-us/library/dd255208(SQL.105).aspx