[PHP] Calling methods from others classes

[Ben Stones]

Hi,

I have this piece of code that I have created:

class userQueries {
    public function numberUsers() {
        $get_users=mysql_query("SELECT * FROM `users` WHERE `online` <
NOW()") or exit("../includes/error.php");
    }
}

class usersOnline extends userQueries {
    public function usersOnline() {
        echo mysql_num_rows($this->numberUsers);
    }
}

How do I request specific methods in other classes? The error that comes up
is:

mysql_num_rows(): supplied argument is not a valid MySQL result resource

which is somewhat expected as $this only refers to the variables and there
are no variables called numberUsers.

Cheers!