Im having gridview with one checkbox1 and the rest is columns, but the vital one is amount column.if I checked 3 checkboxes it must calculate amount based on checked checkboxes

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C#

ASP.NET

Im having gridview with one Checkbox1 and the rest is columns, but the vital one is Amount Column.if I checked 3 checkboxes it must calculate Amount based on checked checkboxes. Any ideas please help

What I have tried:

My gridview

<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">



<asp:TemplateField HeaderText="Company name" Visible="False">
<itemtemplate>
<asp:Label ID="Label4" runat="server" Text='<%# Eval("CallID") %>'>



<edititemtemplate>
<asp:TextBox ID="txtCompanyName" runat="server" Text=' <%# Eval("CallID") %>'>
<asp:RadioButton ID ="txtyes" runat ="server" Text ="" />



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

<edititemtemplate>
<asp:TextBox ID="txtCompanyName" runat="server" Text=' <%# Eval("NewNam") %>'>



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

<edititemtemplate>
<asp:TextBox ID="txtCompanyName" runat="server" Text=' <%# Eval("CalledNo") %>'>




<asp:TemplateField HeaderText="Call Extension">
<itemtemplate>
<asp:Label ID="Label51" runat="server" Text='<%# Eval("CallExt") %>'>

<edititemtemplate>
<asp:TextBox ID="txtPostalAddress" runat="server" Text=' <%# Eval("CallExt") %>'>



<asp:TemplateField HeaderText="Call Duration">
<itemtemplate>
<asp:Label ID="Label6" runat="server" Text='<%# Eval("CallDuration") %>'>

<edititemtemplate>
<asp:TextBox ID="txtResidentialAddress" runat="server" Text=' <%# Eval("CallDuration") %>'>



<asp:TemplateField HeaderText="Amount">
<itemtemplate>
<asp:Label ID="Label7" runat="server" Text='<%# Eval("Amount") %>'>

<edititemtemplate>
<asp:TextBox ID="txtWebSite" runat="server" Text=' <%# Eval("Amount") %>'>



<asp:TemplateField HeaderText="tmpNewNam" Visible="False">
<itemtemplate>
<asp:Label ID="Label50" runat="server" Text='<%# Eval("tmpNewNam") %>'>

<edititemtemplate>
<asp:TextBox ID="txtIfOtherSpecify" runat="server" Text=' <%# Eval("tmpNewNam") %>'>



<emptydatatemplate>
<asp:RadioButton ID="RadioButton1" runat="server" />
 
<asp:RadioButton ID="RadioButton2" runat="server" />



<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();

}
}


Error that i'm getting

Input string was not in a correct format.

Please help. Thanks in advance