Hi folks. Please help

<asp:GridView ID="GridView2" runat="server" OnRowCancelingEdit="GridView1_RowCancelingEdit" OnRowEditing="GridView1_RowEditing" OnRowCommand="GridView1_RowCommand"  OnRowUpdating="GridView1_RowUpdating" DataKeyNames="CallID" AutoGenerateColumns="False" Width="1342px" ShowFooter="True" OnSelectedIndexChanged="GridView1_SelectedIndexChanged" OnRowCreated="GridView1_RowCreated" style="margin-top: 0px" OnRowDataBound="GridView2_RowDataBound">
                            <columns>

<asp:templatefield headertext="">
     <itemtemplate> 
         <asp:CheckBox ID="CheckBox2"   runat="server">
          
     </itemtemplate> 

 <asp:TemplateField HeaderText="Company name" Visible="False">
            <itemtemplate>
        <asp:Label ID="Label4" runat="server" Text='<%# Eval("CallID") %>'>
        <br />
        </itemtemplate>
        <edititemtemplate>
        <asp:TextBox ID="txtCompanyName" runat="server" Text=' <%# Eval("CallID") %>'>
        <asp:RadioButton ID ="txtyes" runat ="server" Text ="" />
        </edititemtemplate>
        

 <asp:TemplateField HeaderText="NewNam">
        <itemtemplate>
        <asp:Label ID="Label5" runat="server" Text='<%# Eval("NewNam") %>'>
        </itemtemplate>
        <edititemtemplate>
        <asp:TextBox ID="txtCompanyName" runat="server" Text=' <%# Eval("NewNam") %>'>
        </edititemtemplate>
        

        <asp:TemplateField HeaderText="Called No">
            <itemtemplate>
        <asp:Label ID="Label61" runat="server" Text='<%# Eval("CalledNo") %>'>
        </itemtemplate>
        <edititemtemplate>
        <asp:TextBox ID="txtCompanyName" runat="server" Text=' <%# Eval("CalledNo") %>'>
        </edititemtemplate>
    
        

        <asp:TemplateField HeaderText="Call Extension">
        <itemtemplate>
        <asp:Label ID="Label51" runat="server" Text='<%# Eval("CallExt") %>'>
        </itemtemplate>
        <edititemtemplate>
        <asp:TextBox ID="txtPostalAddress" runat="server" Text=' <%# Eval("CallExt") %>'>
        </edititemtemplate>
           
                                                             
        <asp:TemplateField HeaderText="Call Duration">
        <itemtemplate>
        <asp:Label ID="Label6" runat="server" Text='<%# Eval("CallDuration") %>'>
        </itemtemplate>
        <edititemtemplate>
        <asp:TextBox ID="txtResidentialAddress" runat="server" Text=' <%# Eval("CallDuration") %>'>
        </edititemtemplate>
            
                                
        <asp:TemplateField HeaderText="Amount">
        <itemtemplate>
        <asp:Label ID="Label7" runat="server" Text='<%# Eval("Amount") %>'>
        </itemtemplate>
        <edititemtemplate>
        <asp:TextBox ID="txtWebSite" runat="server" Text=' <%# Eval("Amount") %>'>
        </edititemtemplate>
       

        <asp:TemplateField HeaderText="tmpNewNam" Visible="False">
        <itemtemplate>
        <asp:Label ID="Label50" runat="server" Text='<%# Eval("tmpNewNam") %>'>
        </itemtemplate>
        <edititemtemplate>
        <asp:TextBox ID="txtIfOtherSpecify" runat="server" Text=' <%# Eval("tmpNewNam") %>'>
        </edititemtemplate>
            
 
                         </columns>
                            <emptydatatemplate>
                                <asp:RadioButton ID="RadioButton1" runat="server" />
                                 
                                <asp:RadioButton ID="RadioButton2" runat="server" />
                                <br />
                            </emptydatatemplate>
                            <HeaderStyle BackColor="#00274F" ForeColor="White" />
                        

Code Behind on button click 

 double sum = 0;
            foreach (GridViewRow gvr in GridView2.Rows)
            {
                CheckBox cb = (CheckBox)gvr.FindControl("CheckBox2");
                if (cb.Checked)
                {
                    double amount = Convert.ToDouble(gvr.Cells[6].Text.Replace(" ", ""));
                    sum += amount;
                }


                txtbusiness.Text = sum.ToString();

            }
        }