ASPxGridView how to multiply two fields in edit mode

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Test.aspx.cs" Inherits="DXWebApplication1.Test" %>  <%@ Register Assembly="DevExpress.Web.v14.1, Version=14.1.6.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" Namespace="DevExpress.Web.ASPxEditors" TagPrefix="dx" %>  <%@ Register Assembly="DevExpress.Web.v14.1, Version=14.1.6.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" Namespace="DevExpress.Web.ASPxGridView" TagPrefix="dx" %>     xmlns="http://www.w3.org/1999/xhtml">  runat="server">           src="Scripts/jquery-1.8.2.js">      src="Scripts/jquery-1.4.1.min.js">        type="text/javascript">         $(function () {             $("#ASPxGridView1").find("input[title='item_quantity']").blur(function () {                 var item_quantity = $(this).val();                 var item_price = $("#ASPxGridView1").find("input[title='item_price']").val();                 if (item_quantity != "" && item_price != "") {                     var total = parseInt(item_price) + parseInt(item_quantity);                     $("#ASPxGridView1").find("input[title='item_amount']").val(total);                 } else {                     $("#ASPxGridView1").find("input[title='item_amount']").val("");                 }             })         })            type="text/javascript">          function DoProcessEnterKey(htmlEvent, editName) {             if (htmlEvent.keyCode == 13 && editName == "textbox1") {                 ASPxClientUtils.PreventEventAndBubble(htmlEvent);                 btn.DoClick();              }             if (htmlEvent.keyCode == 13 && editName == "textbox4") {                 ASPxClientUtils.PreventEventAndBubble(htmlEvent);                 btn_price.DoClick();               }         }                 ID="ASPxGridView1" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1" EnableTheming="True" KeyFieldName="transaction_id" OnRowCommand="ASPxGridView1_RowCommand" OnRowUpdated="ASPxGridView1_RowUpdated" OnRowUpdating="ASPxGridView1_RowUpdating" Theme="Metropolis">                                                       ShowDeleteButton="True" ShowEditButton="True" VisibleIndex="0">                                                           FieldName="item_number" VisibleIndex="1">                                                           FieldName="item_description" VisibleIndex="2">                                                           FieldName="item_unit" VisibleIndex="3">                                                           FieldName="item_quantity" VisibleIndex="4">                                                           FieldName="item_price" VisibleIndex="5">                                                           FieldName="item_amount" VisibleIndex="6">                                                           FieldName="voucher_number" VisibleIndex="7">                                                                                ConfirmDelete="True" />                          Mode="PopupEditForm">                                                   ShowFilterRow="True" ShowFooter="True" />                                                                  />              <%$ ConnectionStrings:item_detailConnectionString %>" DeleteCommand="DELETE FROM [tbl_item_detail_transactions] WHERE [transaction_id] = @transaction_id" InsertCommand="INSERT INTO [tbl_item_detail_transactions] ([item_number], [item_description], [item_unit], [item_quantity], [item_price], [item_amount], [voucher_number]) VALUES (@item_number, @item_description, @item_unit, @item_quantity, @item_price, @item_amount, @voucher_number)" SelectCommand="SELECT  *, (item_quantity * item_price) as item_amount2 FROM [tbl_item_detail_transactions]" UpdateCommand="UPDATE [tbl_item_detail_transactions] SET [item_number] = @item_number, [item_description] = @item_description, [item_unit] = @item_unit, [item_quantity] = @item_quantity, [item_price] = @item_price, [item_amount] = @item_amount, [voucher_number] = @voucher_number WHERE [transaction_id] = @transaction_id">                                       Name="transaction_id" Type="Int32" />                                                        Name="item_number" Type="Int32" />                      Name="item_description" Type="String" />                      Name="item_unit" Type="Int32" />                      Name="item_quantity" Type="Int32" />                      Name="item_price" Type="Int32" />                      Name="item_amount2" Type="Int32" />                      Name="voucher_number" Type="Int32" />                                                        Name="item_number" Type="Int32" />                      Name="item_description" Type="String" />                      Name="item_unit" Type="Int32" />                      Name="item_quantity" Type="Int32" />                      Name="item_price" Type="Int32" />                      Name="item_amount" Type="Int32" />                      Name="voucher_number" Type="Int32" />                      Name="transaction_id" Type="Int32" />