CREATE TABLE table_name_91 (airing_date VARCHAR2, number_of_episodes VARCHAR2, genre VARCHAR2)

What is the airing date for costume comedy that has 20 episodes?
SELECT airing_date FROM table_name_91 WHERE number_of_episodes = 20 AND genre = "costume comedy"
SELECT "airing_date" FROM "table_name_91" WHERE "costume comedy" = "genre" AND "number_of_episodes" = 20