What is the average education level of customers from the place with the highest average income per month?
place with the highest average income per month refers to GEOID where MAX(INCOME_K); average education level refers to AVG(EDUCATIONNUM);
SELECT AVG(T1.EDUCATIONNUM) FROM Customers AS T1 INNER JOIN Demog AS T2 ON T1.GEOID = T2.GEOID ORDER BY T2.INCOME_K DESC LIMIT 1