Value to append in query string

Hi,
I want to append value of textbox in a query string with the value of hidden field also to be included in query string on button click. i implemented with hidden field. See my code for your reference.
<p class="parae"> Enter the last 5 digits of your RBL Bank Credit Card<span> <asp:TextBox ID="txtCredtCard" runat="server" MaxLength="5" CssClass="txtboxe"></asp:TextBox> <asp:RequiredFieldValidator ID="reqText" runat="server" ErrorMessage="please enter 5 digit number" ControlToValidate="txtCredtCard"></asp:RequiredFieldValidator> <asp:RegularExpressionValidator ID="regText" runat="server" ErrorMessage="please enter only 5 digit numbers" ValidationExpression="^[0-9]{5}$" ControlToValida ...