Javascript or Jquery auto populate one input text based on another input value
<p>I am not good at JS or Jquery. I take the follow code for better explaining what I what. When a user input 400 or more to triglycerides, the LDL is autopopulated with 'N/A'. How do I implement JS or Jqeury to do that? thanks</p>

<pre><code>&lt;form&gt;
 &lt;input name='triglycerides" value="" /&gt;
 &lt;input name='LDL' value="" /&gt;
&lt;/form&gt;
</code></pre>

<p>My actual code is as follows:</p>

<pre><code>$('#ldl_override').keyup(function(){
var val = parseInt($(this).val());
if(val &gt; 399)
   $('#qIn726').val('N/A');
});


 elseif($ldl_override &amp;&amp; $questionID == 728)
 {
  $question .= "&lt;input $maxLengthString id=\"ldl_override\" name=\"field[" . $questionID . "]\" type=\"text\" value=\"" . htmlspecialchars($answer) . "\" /&gt;\n";
 }
</code></pre>
