who are the directors of the episode that had 20.5 millions of north american viewers? 
CREATE TABLE table_27714573_1 (directed_by VARCHAR, us_viewers__millions_ VARCHAR)
SELECT directed_by FROM table_27714573_1 WHERE us_viewers__millions_ = "20.5"
<s>[INST] Write mssql query to answer the following question given the database schema. Schema: CREATE TABLE table_27714573_1 (directed_by VARCHAR, us_viewers__millions_ VARCHAR) Question: who are the directors of the episode that had 20.5 millions of north american viewers?  [/INST] SELECT directed_by FROM table_27714573_1 WHERE us_viewers__millions_ = "20.5" </s>