Database: trains
Question: How many cars running east have double-sided tail cars?
SQL: SELECT COUNT(T1.id) FROM trains AS T1 INNER JOIN cars AS T2 ON T1.id = T2.train_id INNER JOIN ( SELECT train_id, MAX(position) AS trailPosi FROM cars GROUP BY train_id ) AS T3 ON T1.id = T3.train_id WHERE T1.direction = 'east' AND T2.position = T3.trailPosi AND T2.sides = 'double'