CREATE TABLE "table1_21979779_1" (
  "no" real,
  "num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);

Question: who are the writers of the episode that had 3.07 millions of North American spectators?
SQL: SELECT "written_by" FROM "table1_21979779_1" WHERE "u_s_viewers_million"='3.07';

Question: what is the biggest series episode number whose production code is 2t7211?
SQL: SELECT MAX("no") FROM "table1_21979779_1" WHERE "production_code"='2T7211';

Question: what is the smallest series episode number whose production code is 2t7211?
SQL: SELECT MIN("no") FROM "table1_21979779_1" WHERE "production_code"='2T7211';

Question: when was the premiere of the episode where the amount of North American spectators was 1.76 millions?
SQL: SELECT "original_air_date" FROM "table1_21979779_1" WHERE "u_s_viewers_million"='1.76';