jQuery hide

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">

<head>
   <meta http-equiv="content-type" content="text/html; charset=cp1250" />
   <meta name="author" content="Peter Dräxler" />
    <script src="http://code.jquery.com/jquery-latest.pack.js"></script>
   <title>jQuery pokusy</title>
   
    <script>
    $("a .ahide").click(function(){ 
    $(".hide").hide();
    });
    </script>
</head>

<body>
<a href="#">SHOW</a>, <a href="#" class="ahide">HIDE</a>
<br />
<span class="hide">
:(
</span>
</body>
</html>

 $(document).ready(function(){});

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">

<head>
   <meta http-equiv="content-type" content="text/html; charset=cp1250" />
   <meta name="author" content="Peter Dräxler" />
    <script src="http://code.jquery.com/jquery-latest.pack.js"></script>
   <title>jQuery pokusy</title>
   
    <script>
    $(document).ready(function(){
   
    $(".sposob_platby").change(function(){ 
    var sposob_platby = getElementsById("hide");
     if (document.getElementById('3').checked) {
    $(".hide").hide();
    }
    });
   
    });
    </script>
</head>

<body>
<select class="sposob_platby">
<option value="LoL">LoL</option>
<option value="HA!">HA!</option>
<option value="3">Chi!</option>
</select>
<div id="hide">CHi!</div>
</body>
</html>

   
document.getElementById("3") is null
[Break on this error] if (document.getElementById('3').checked) {\r\n

$(".sposob_platby").change(function(){   
  if(this.value==3) {
    $("#hide").hide();
  }
});

 $(".sposob_platby").change(function(){ 
            if ($(this).val()=='3') {
              $(".hide").hide();
            }
           });