[C#] Textbox in Alert Box

Hi, I have a question to ask..
Im using c#, and this is the alert box for registration form submission...
ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "success", "alert('Order Successfully!!');window.location='../Classic.aspx';", true);
and I want to make one of the textbox from the registration form to be presented in the alert box as well...
txtTrackNumber.Text does anybody know how to do this? Thanks in advance...
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