Plus two columns in one column in gridview C#

<asp:TemplateField HeaderText="GST%" HeaderStyle-Width="15%" SortExpression="cgstPer">
                                   <ItemTemplate>
                                       <asp:Label ID="lblcgstPer" runat="server" Text='<%# Eval("cgstPer") %>'></asp:Label>

                                   </ItemTemplate>
                                   <HeaderStyle HorizontalAlign="Left"></HeaderStyle>
                                   <ItemStyle HorizontalAlign="Left"></ItemStyle>
                               </asp:TemplateField>
                               <asp:TemplateField HeaderText="totalGst" HeaderStyle-Width="15%" SortExpression="aferDiscountValue">
                                   <ItemTemplate>
                                       <asp:Label ID="lblcgstPer" runat="server" Text='<%# Eval("cgstPer") %>'></asp:Label>

                                   </ItemTemplate>
                                   <HeaderStyle HorizontalAlign="Left"></HeaderStyle>
                                   <ItemStyle HorizontalAlign="Left"></ItemStyle>
                               </asp:TemplateField>

<asp:Label ID="lblcgstPer" runat="server" Text='<%#Convert.ToInt32(Eval("cgstPer")) +Convert.ToInt32(Eval("sgstPer")) %>'></asp:Label>