Too easy but failed - get the top position of each td after AJAX response

Too easy but failed - get the top position of each td after AJAX response

Just give me a little hint
how can I get 
            alert('top=='+evto);


[index.php]---------------------------------------------------
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
       
    <title>Loop through an array using jQuery</title>
        <script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
    
    <script type="text/javascript">
           
$(document).ready(function () {
          var dataj ={'ss':'ss', 'tss':'tss'};

                 $.ajax({
                         type: "POST", 
                          url: "prc_treach.php",
                         data: dataj,
                         cache: false,
                         success: function(html) {
                             $(" #right_td").html(html);
                        }   
                             
                 });//ajax

$(" #right_td").delegate(' #tbl_write tr', each(function() {

   var ev = $(this).offset();
   var evto = ev.top;
 
    alert('top=='+evto);

});//#tbl
});//doc

</script>
</head>
<body>
<div id=" right_td"></div>
</body>
</html>

[prc_treach.php]-----------------------------------------
<?php

echo '<table id="tbl_write">';
echo '<tr><td>fefefe</td><td>efefe</td><td>efefe</td></tr>';
echo '<tr><td>fefefe</td><td>efefe</td><td>efefe</td></tr>';
echo '<tr><td>fefefe</td><td>efefe</td><td>efefe</td></tr>';
echo '<tr><td>fefefe</td><td>efefe</td><td>efefe</td></tr>';
echo '</table>';

?>