The calculation of $27 + $2 contains two errors: the manager's $5 is ignored and the bellboy's $2 is counted in the wrong direction. The original payment of $30 is correctly accounted for as $27 finally paid by the three guests, plus $5 refunded by the manager, MINUS $2 kept by the bellboy (so that only $3 of refund was received).

lib/DbaDatabase.php:134: Warning: dba_replace() [<a href='function.dba-replace'>function.dba-replace</a>]: You cannot perform a modification to a database without proper access