Insert data into table- simple problrm

Hi!
I posted the data in this script from a form - the variables in this code stored the data inserted from the textboxes in the form.
from some reasom this doesn't work.

Any Idea?

<?php
$x = $_POST['name'];
$y = $_POST['age'];
$z= $_POST['subject'];

$mysql_link= mysql_connect('localhost','root','') or die("ERROR:cannot connect");
echo "connected successfully to MySQL server.";

mysql_select_db('pets',$mysql_link) or die ("could not open db".mysql_error());
echo "connected successfully to pets.";

mysql_query("INSERT INTO students (name, age, subject) 
VALUES ($x, $y, $z)"); 
mysql_close($mysql_link);
?>

PHP:

 

Try:

VALUES ('$x', '$y', '$z)');

 

And PLEASE escape your data...