CREATE TABLE table_27714573_1 (directed_by VARCHAR2, us_viewers__millions_ VARCHAR2)

who are the directors of the episode that had 20.5 millions of north american viewers?
SELECT directed_by FROM table_27714573_1 WHERE us_viewers__millions_ = "20.5"
SELECT "directed_by" FROM "table_27714573_1" WHERE "20.5" = "us_viewers__millions_"