$(document).ready( 
  function(){ 

    $("input[@name='Answer17']").click(
      function()
      {
        if ($("input[@name='Answer17']:checked").val() == "Yes") {
          $("input[@name='Answer18']").val($("input[name='Answer3']").val());
          $("input[@name='Answer19']").val($("input[name='Answer4']").val());
          $("input[@name='Answer20']").val($("input[name='Answer5']").val());
          $("input[@name='Answer21']").val($("input[name='Answer6']").val());
        } else {
          $("input[@name='Answer18']").val('');
          $("input[@name='Answer19']").val('');
          $("input[@name='Answer20']").val('');
          $("input[@name='Answer21']").val('');
        }
      }
    );
  }
);