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<html>

<head>

  <meta http-equiv="content-type" content="text/html; charset=UTF-8">

  <title></title>

  <meta http-equiv="content-type" content="text/html; charset=UTF-8">

  <meta name="robots" content="noindex, nofollow">

  <meta name="googlebot" content="noindex, nofollow">

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  <script

    type="text/javascript"

    src="//code.jquery.com/jquery-2.1.3.js">

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</head>

<body>

    <select name="status" id ="combo">

      <option value="_">Please choose..</option>

        <option  value="Pending">Pending</option>

        <option  value="Process">Process</option>

        <option  value="Delivered" >Delivered</option>

      </select>

 <tr valign="baseline">

 <td nowrap="nowrap" align="right" class="postage">Postage:</td>

 <input type="text" name="aaa" id="textbox" disabled>

 <input type="text" name="bbb" id="textboxnew" disabled>



    <script type="text/javascript">//<![CDATA[





$(document).on('change', '#combo', function(){

    var shouldEnable = $(this).val() !== 'Delivered';

    $('#textbox').prop('disabled', shouldEnable);



});





  //]]></script>



 



</body>

</html>