Question: In which ward of more than 55,000 inhabitants are there more crimes of intimidation with extortion?
SQL: SELECT T3.ward_no FROM IUCR AS T1 INNER JOIN Crime AS T2 ON T2.iucr_no = T1.iucr_no INNER JOIN Ward AS T3 ON T3.ward_no = T2.ward_no WHERE T1.primary_description = 'INTIMIDATION' AND T1.secondary_description = 'EXTORTION' AND T3.Population > 55000 GROUP BY T3.ward_no ORDER BY COUNT(T3.ward_no) DESC LIMIT 1