sum in subreport

Hi all,
I have aCrystal Reportreport that showsthe data like this:
product  price  qty      Vat
1020      10,00     2        10
1050      20,00     1       10
1060      30,00     1        20
1080      50,00    2        20


andin the footer I havea subreport thatIgroupsaccording toVat,then
price     Vat
40,00      10
130,00    20


I wanta field that summarizesprice, so:
price      vat
40,00     10
130,00    20
tot.price175.00


how do you?

thank you very much

bye