user: Question: What were the air-dates of the episodes before episode 4 that had a BBC One weekly ranking of 6?
Columns: ['Episode No.', 'Airdate', 'Total Viewers', 'Share', 'BBC One Weekly Ranking']
Types: ['real', 'text', 'real', 'text', 'real']
Sample row: [1.0, '8 April 2010', 6700000.0, '24.8%', 6.0]
SQL:

assistant: SELECT "Airdate" FROM "Table" WHERE "Episode No." < 4.0 AND "BBC One Weekly Ranking" = 6.0;