What is the occupation of customers within number of inhabitants ranges of 30 to 40?
number of inhabitants ranges of 30 to 40 refers to INHABITANTS_K BETWEEN 30 AND 40;
SELECT DISTINCT T1.OCCUPATION FROM Customers AS T1 INNER JOIN Demog AS T2 ON T1.GEOID = T2.GEOID WHERE T2.INHABITANTS_K >= 30 AND T2.INHABITANTS_K <= 40