how to multiply GridView Column in asp.net using javascript or jquery

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ASP.NET

Javascript

jQuery

C#3.5

<asp:GridView ID="GvOrder" runat="server" AutoGenerateColumns="false">
        <Columns>

               <asp:TemplateField HeaderText = "Item">
                <ItemTemplate>
                    <asp:Label ID="lblItemName" runat="server" Text='<%# Eval("Product_Name")%>' ></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
             <asp:TemplateField HeaderText = "Price">
                <ItemTemplate>
                    <asp:Label ID="lblPrice" runat="server" Text='<%# Eval("Unit_Price")%>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
             <asp:TemplateField HeaderText = "Quantity">
                <ItemTemplate>
                    <asp:TextBox ID="txtQuantity"  onkeyup="return calculate(this)" runat="server"></asp:TextBox>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText = "Total">
                <ItemTemplate>
                    <asp:Label ID="lblTotal" runat="server" Text="0"></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>

item,Price,Total and grandtotal are label field and Quantity is in textbox
when we enter quantity then total and grand total will immediately calculate and display.
and when we erase quantity means no value then total and grand total will be immediately 0. how is it possible please help .