Как добавить нижний колонтитул в сетку

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Я пытаюсь добавить нижний колонтитул в gridview, чтобы вычислить общий балл.

любая помощь, пожалуйста.

Что я уже пробовал:

<asp:GridView ID="GVDuties" runat="server" AllowPaging="True" AutoGenerateColumns="False" BackColor="LightGoldenrodYellow" BorderColor="Tan" BorderWidth="1px" CellPadding="2" DataKeyNames="ID" DataSourceID="SqlGVDuties" ForeColor="Black" GridLines="None" OnRowDataBound="GVDuties_RowDataBound" OnSelectedIndexChanged="GVDuties_SelectedIndexChanged">
        <AlternatingRowStyle BackColor="PaleGoldenrod" />
        <Columns>
            <asp:CommandField ShowSelectButton="True" />
            <asp:BoundField DataField="ID" HeaderText="ID" InsertVisible="False" ReadOnly="True" SortExpression="ID" Visible="False" />
            <asp:BoundField DataField="Duties" HeaderText="Duties" SortExpression="Duties" />
            <asp:BoundField DataField="Agreed" HeaderText="Agreed" SortExpression="Agreed" />
            <asp:BoundField DataField="Score" HeaderText="Score" SortExpression="Score" />
            <asp:BoundField DataField="Comment" HeaderText="Comment" SortExpression="Comment" />
            <asp:BoundField DataField="EP" HeaderText="EP" SortExpression="EP" Visible="False" />
           <!-- trying to add footer
             <footertemplate>
      <asp:TextBox id="TestTbx"   runat="server"/>
     </footertemplate>
     -->
        </Columns>
        <FooterStyle BackColor="Tan" />
        <HeaderStyle BackColor="Tan" Font-Bold="True" />
        <PagerStyle BackColor="PaleGoldenrod" ForeColor="DarkSlateBlue" HorizontalAlign="Center" />
        <SelectedRowStyle BackColor="DarkSlateBlue" ForeColor="GhostWhite" />
        <SortedAscendingCellStyle BackColor="#FAFAE7" />
        <SortedAscendingHeaderStyle BackColor="#DAC09E" />
        <SortedDescendingCellStyle BackColor="#E1DB9C" />
        <SortedDescendingHeaderStyle BackColor="#C2A47B" />

    </asp:GridView>

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