What were the air-dates of the episodes before episode 4 that had a BBC One weekly ranking of 6?
CREATE TABLE "series_3" (
  "episode_no" real,
  "airdate" text,
  "total_viewers" real,
  "share" text,
  "bbc_one_weekly_ranking" real
);
SELECT "airdate" FROM "series_3" WHERE "episode_no"<4 AND "bbc_one_weekly_ranking"=6;