Question Updating a calculated field after updating a Datagrid

[Juan Navarrete]

I have been writing a web store using VB in VS2010. I have a detail file which one of he fields is 'Total', calculated by multiplying quantity * Price. This works fine when adding to the cart. In the shopping cart page, I have a data grid which shows the items in the cart and each line has an update button to update when the quantity is changed. The quantity is written without a problem but the 'Total' field is nulled out. How can I update the total for the line? I have tried 'RowUpdated' and 'Rowupdating' but does not work as intended.

Any help is appreciated.