VB.Net ขอถามเรื่อง อยากให้ datagrid คำนวน ราคาสินค้า

Private Sub Buttonexport_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Buttonexport.Click

Dim xlapp As New excel.Application

        Dim xlappCo As New excel.ApplicationCode


        Dim ra As excel.Range



        On Error Resume Next

        xlapp = CType(GetObject(, "Excel.Application"), excel.Application)

        xlappCo = CType(GetObject(, "Excel.Application"), excel.Application)

        If Err.Number <> 0 Then

            xlapp = New excel.Application

        End If

        xlapp.Visible = True

        xlapp.Workbooks.Add()

        ra = xlapp.ActiveCell


        With DGVTest

            For i As Integer = 0 To .RowCount - 1
                For j As Integer = 0 To .ColumnCount - 1


                    ra.Offset(i + 1, j).Value = .Rows(i).Cells(j).Value


                Next

            Next
   

        End With
End Sub