Question: How many trains running west have double sided cars in 3rd position?
SQL: SELECT COUNT(T.train_id) FROM (SELECT T1.train_id FROM cars AS T1 INNER JOIN trains AS T2 ON T1.train_id = T2.id WHERE T1.position = 3 AND T2.direction = 'west' AND T1.sides = 'double' GROUP BY T1.train_id)as T