if (Drupal.jsEnabled) {
  $(document).ready(function(){
    var query = $(".captcha span.field-prefix").text();
    var first = query.substr(0, 2);
    var second = query.substr(4, 2);
    first = $.trim(first);
    second = $.trim(second);
    var result = parseInt(first) + parseInt(second);
    $("#edit-captcha-response").attr("value", result);
    $("fieldset.captcha").hide();
    return false;
  }); 
}