Custom Page with Custom PHP tags

[Zukran]

So I've managed to create a custom php for my website using this method:https://vborg.vbsupport.ru/showthread.php?t=228112 and it works great! I've done some searching and I can't seem to find a way to use php on such a page.

I need to be able to use php and call to a external database outside of the forums database also using GET attributes. Example code I need to use:

PHP Code:

mysql_connect("host", "username", "pasword") or die(mysql_error());
//Connects to the database
mysql_select_db("database") or die(mysql_error());

$id = $_GET["id"];


$result = mysql_query("SELECT * FROM database WHERE id ='$id'");
while ($row = mysql_fetch_assoc($result))
{
$population= $row['population'];
}
echo "$population and $id"; 


I've tried including this in the template area designated by the thread I posted above but it doesn't seem to respond to php. Does any one know if its possible in add php to custom pages? and how?

Thank-you in advance!

Ryan