if input >= 5 : display the tab4 > from php code to jquery please

if input >= 5 : display the tab4 > from php code to jquery please

hi
i have 4 tabs and i want that the 4th is not visible when the <input type="text" name="field" /> is below 5.

i have now the following in php what i want to change to jquery-code
<?if(isset( $_POST [ 'checken_if_bigger_than_5' ]))
{ 
   if(
$_POST['field'] >= 5) 
   { 
$display = "visiblity:visible";}  
}
else 
{
   $display= "display: none";
} 
# en here is where the display variabel is coming
<div id="tab-4" style="'.$display.'"> 
?>
because with php you have to submit the form before he can check if the input >= 5 and check what the visibility must be. i want to change it to jquery code but i dunnow how..
please, can someone help?
regards