Of customers who provide other services, how many are from places where inhabitants are more than 20000?
OCCUPATION = 'Other-service'; inhabitants are more than 20000 refer to INHABITANTS_K > 20;
SELECT COUNT(T2.GEOID) FROM Customers AS T1 INNER JOIN Demog AS T2 ON T1.GEOID = T2.GEOID WHERE T1.OCCUPATION = 'Other-service' AND T2.INHABITANTS_K > 20