CREATE TABLE table_21979779_1 (written_by VARCHAR, us_viewers__million_ VARCHAR)

who are the writers of the episode that had 3.07 millions of North American spectators?
SELECT written_by FROM table_21979779_1 WHERE us_viewers__million_ = "3.07"
SELECT "written_by" FROM "table_21979779_1" WHERE "3.07" = "us_viewers__million_"