PHP SQL Variables

Trying to make an update to two tables at once using PHP but the tables have foreign keys linking them. Normally I would set an @variable with LAST_INSERT_ID() but this won't work within the PHP code.

$newclass = "INSERT INTO PT_Classes(`Title`, `Details`, `Location`, `Time`, `Date`) 
        VALUES ('$title', '$details', '$location','$ntime', '$ndate'); 
        SET @last_id_PT_Classes = LAST_INSERT_ID();
        INSERT INTO PT_Calendar(`Date`, `Class`, `Details`) 
        VALUES ('$ndate', @last_id_PT_Classes,'$title');
        ";

however keep getting a "You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'SET @last_id_PT_Classes = LAST_INSERT_ID(); INSERT INTO PT_Calendar(`Dat' at line 3"

Anyone know a way around this?