i have answered this question in the private msg.. but well..
u can create a formula, let's call it sum1.
using the formula editor, write the field bounded by textbox 1 and textbox 2
example if textbox1 is price1 in tableA and textbox2 is price2 in tableB, type:
{tableA.price1} + {tableB.price2}
and click save and close
then drag the formula sum1 into the detail section of your report
