Calculating product quantity*rate=amount in gridview

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C#2.0

ASP.NET

SQL

server

on selecting dropdown list in gridview its rate has to be displayed in label of that row, in the same row quantity column is to make user to enter quantity in textbox. and the amount has to be displayed by calculating quantity* rate . and this gridview must be autogenerated.

What I have tried:

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
                DataSourceID="SqlDataSource2" 
                 
                ShowHeaderWhenEmpty="True" ShowFooter="True"
                Width="595px" onselectedindexchanged="GridView1_SelectedIndexChanged" 
                ondatabinding="Page_Load">
                <columns>
                    <asp:TemplateField HeaderText="Sno" SortExpression="Sno">
                    
                        <edititemtemplate>
                            <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("Sno") %>'>
                        
                        <itemtemplate>
                            <asp:Label ID="Label1" runat="server" Text='<%# Bind("Sno") %>'>
                        
                        <footertemplate>
                            <asp:LinkButton ID="LinkButton1" runat="server">Insert
                        
                        
                        
                    
                    <asp:TemplateField HeaderText="Product" SortExpression="Product">
                        
                        <itemtemplate>
                            <asp:Label ID="Labelt" runat="server" Text='<%# Bind("Product") %>'>
                        
                        <footertemplate>
                            <asp:DropDownList runat="server" DataSourceID="slsfConnectionString3" DataValueField="Prid"  DataTextField="Product" Id="ddp">
                             
                        
                    
                    <asp:TemplateField HeaderText="Quantity" SortExpression="Quantity">
                        
                        <itemtemplate>
                            <asp:Label ID="Label2" runat="server" Text='<%# Bind("Quantity") %>'>
                        
                        <footertemplate>
                        <asp:TextBox ID="TextBox2" runat="server" Text='<%# Bind("Quantity") %>'>
                        
                    
                    <asp:TemplateField HeaderText="Rate" SortExpression="Rate">
                        <footertemplate>
                            <asp:Label ID="Label5" runat="server" Text='<%# Bind("Rate") %>' >
                        
                        <itemtemplate>
                            <asp:Label ID="Label3" runat="server" Text='<%# Bind("Rate") %>'>
                        
                    

                    <asp:TemplateField HeaderText="Amount" SortExpression="Amount">

                        <edititemtemplate>
                            <asp:TextBox ID="TextBox4" runat="server" Text='<%# Bind("Amount") %>'>
                        
                        <itemtemplate>
                            <asp:Label ID="Label4" runat="server" Text='<%# Bind("Amount") %>'>
                        
                        <footertemplate>
                        <asp:Label ID="Label6" runat="server" Text='<%# Eval("Amount") %>'>