Parse error: syntax error, unexpected '=' in

Hi. everyone.

Please help me.
I added a php buttom on a form for recalculation of parent table and child table.
I want to sum of basepay in paymst table, and want to update basepay in summary table.

sql = “update summary set basepay=(SELECT SUM(basepay) FROM paymst WHERE sumid = 6) where sumid = 6”;

How do I fix?

Thank you.