ต้องการทราบผลรวมจากคอลั่มใน Datagrid ขอทราบแนวทางหรือโค๊ดหน่อยครับ

Imports System.Data.SqlClient
Imports System.Threading
Imports System.Globalization

Public Class Form1

    Dim resp As MsgBoxResult

    Dim a1 As Integer = "10000"
    Dim a2 As Integer = "3000"
    Dim a3 As Integer = "13000"
    Dim a4 As Integer = "50000"

    Dim b1 As Integer = "11250"
    Dim b2 As Integer = "3250"
    Dim b3 As Integer = "14000"
    Dim b4 As Integer = "56000"

    Dim c1 As Integer = "12500"
    Dim c2 As Integer = "3500"
    Dim c3 As Integer = "16000"
    Dim c4 As Integer = "63000"

    Dim d1 As Integer = "13250"
    Dim d2 As Integer = "3750"
    Dim d3 As Integer = "17000"
    Dim d4 As Integer = "66000"

    Dim e1 As Integer = "14000"
    Dim e2 As Integer = "4000"
    Dim e3 As Integer = "18000"
    Dim e4 As Integer = "70000"

    Dim f1 As Integer = "15000"
    Dim f2 As Integer = "4000"
    Dim f3 As Integer = "19000"
    Dim f4 As Integer = "75000"

    Dim g1 As Integer = "16000"
    Dim g2 As Integer = "4500"
    Dim g3 As Integer = "20500"
    Dim g4 As Integer = "80000"

    Dim h1 As Integer = "20000"
    Dim h2 As Integer = "5000"
    Dim h3 As Integer = "25000"
    Dim h4 As Integer = "100000"

    Dim i1 As Integer = "22500"
    Dim i2 As Integer = "6000"
    Dim i3 As Integer = "28500"
    Dim i4 As Integer = "110000"

    Dim j1 As Integer = "25000"
    Dim j2 As Integer = "7000"
    Dim j3 As Integer = "32000"
    Dim j4 As Integer = "125000"

    Dim com As String = "Completed"
    Dim wai As String = "Waiting"


    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        Dim casee As String = ""



        If RB1.Checked Then
            txt1.Text = a1
            txt2.Text = a2
            txt3.Text = a3
            txt4.Text = a4
        ElseIf RB2.Checked Then
            txt1.Text = b1
            txt2.Text = b2
            txt3.Text = b3
            txt4.Text = b4
        ElseIf RB3.Checked Then
            txt1.Text = c1
            txt2.Text = c2
            txt3.Text = c3
            txt4.Text = c4
        ElseIf RB4.Checked Then
            txt1.Text = d1
            txt2.Text = d2
            txt3.Text = d3
            txt4.Text = d4
        ElseIf RB5.Checked Then
            txt1.Text = e1
            txt2.Text = e2
            txt3.Text = e3
            txt4.Text = e4
        ElseIf RB6.Checked Then
            txt1.Text = f1
            txt2.Text = f2
            txt3.Text = f3
            txt4.Text = f4
        ElseIf RB7.Checked Then
            txt1.Text = g1
            txt2.Text = g2
            txt3.Text = g3
            txt4.Text = g4
        ElseIf RB8.Checked Then
            txt1.Text = h1
            txt2.Text = h2
            txt3.Text = h3
            txt4.Text = h4
        ElseIf RB9.Checked Then
            txt1.Text = i1
            txt2.Text = i2
            txt3.Text = i3
            txt4.Text = i4
        ElseIf RB10.Checked Then
            txt1.Text = j1
            txt2.Text = j2
            txt3.Text = j3
            txt4.Text = j4
        End If


    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        nameasset()
        statussalary()
        change_all_column()
    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        Me.Close()
    End Sub

    Private Sub change_all_column()
        Dim header() As String = {"รหัสงาน", "ชื่อ", "ค่าบริการ"}
        change_column_datagrid(DGV1, header)
    End Sub

    Private Sub nameasset()
        If cn.State = ConnectionState.Open Then cn.Close()
        'cn.ConnectionString = sql
        connect_open()

        Dim sql1 As String = "SELECT CUSTID,USER_ASSess FROM TBL_POLICY_SUCCESS"
        'Dim sql1 As String = "SELECT OFFICER_ID,FNAME_THAI FROM TBL_OFFICER"

        Dim da As New SqlDataAdapter(sql1, cn)


        Dim dt As New DataTable
        da.Fill(dt)

        With cbb1
            .DataSource = dt
            .DisplayMember = dt.Columns.Item("USER_ASSess").ColumnName
            .ValueMember = dt.Columns.Item("CUSTID").ColumnName

        End With
    End Sub

    Private Sub statussalary()
        If cn.State = ConnectionState.Open Then cn.Close()
        'cn.ConnectionString = sql
        connect_open()

        Dim sql1 As String = "SELECT cus,status FROM Status_Salary"
        'Dim sql1 As String = "SELECT OFFICER_ID,FNAME_THAI FROM TBL_OFFICER"

        Dim da As New SqlDataAdapter(sql1, cn)


        Dim dt As New DataTable
        da.Fill(dt)

        With cbb2
            .DataSource = dt
            .DisplayMember = dt.Columns.Item("status").ColumnName
            .ValueMember = dt.Columns.Item("cus").ColumnName

        End With
    End Sub



    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
       
        names.Text = cbb1.Text
        sql = "select CERTIFICATE,NAME,TOTALPRICE from TBL_POLICY_SUCCESS where STATUS_REPORT1 = '" & cbb2.Text & "' AND TBL_POLICY_SUCCESS.USER_ASSess = '" & cbb1.Text & "'  "
        DGV1.DataSource = cmd_dataTable()

        ' AND TBL_POLICY_SUCCESS.SENT_REPORT_DATE like '" & dtp_1.Value.ToString("yyyy-MM-dd HH:mm:ss.ttt") & "'
    End Sub


    Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
        GirdToExcel(DGV1)
    End Sub

    Private Sub GirdToExcel(ByRef dgvw As DataGridView)
        Dim Appli As New Microsoft.Office.Interop.Excel.Application
        Dim Libro As Microsoft.Office.Interop.Excel.Workbook
        Dim Hoja As Microsoft.Office.Interop.Excel.Worksheet
        Dim col As Integer = DGV1.ColumnCount
        Dim row As Integer = DGV1.RowCount
        Libro = Appli.Workbooks.Add
        Hoja = Appli.Worksheets.Add()

        For i As Integer = 1 To col
            Hoja.Cells.Item(1, i) = DGV1.Columns(i - 1).Name.ToString
        Next
        For fila As Integer = 0 To row - 1
            For e As Integer = 0 To col - 1
                Hoja.Cells.Item(fila + 2, e + 1) = DGV1.Rows(fila).Cells(e).Value
            Next
        Next
        Hoja.Rows.Item(1).font.bold = 1
        Hoja.Rows.Item(1).horizontalAlignment = 3
        Hoja.Columns.AutoFit()
        Appli.Application.Visible = True
        Appli.Application.WindowState = Microsoft.Office.Interop.Excel.XlWindowState.xlMaximized
        Hoja = Nothing
        Libro = Nothing
        Appli = Nothing


    End Sub


    Private Sub DGV1_CellContentClick(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DGV1.CellContentClick
    End Sub

    Private Sub Button7_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button7.Click
        If DGV1.RowCount > 1 Then
            Dim iTax As Integer = 0

            For index As Integer = 0 To DGV1.RowCount - 1
                iTax += Convert.ToInt32(DGV1.Rows(index).Cells(0).Value)
            Next
            Label5.Text = iTax
        End If
    End Sub
End Class