What is the average salary of the worst performing managers?
the worst performing refers to performance = 'Poor'; manager is a positiontitle; average salary refers to AVG(salary)
SELECT AVG(CAST(REPLACE(SUBSTR(T1.salary, 4), ',', '') AS REAL)) FROM employee AS T1 INNER JOIN position AS T2  ON T1.positionID = T2.positionID WHERE T1.performance = 'Poor' AND T2.positiontitle = 'Manager'