CREATE TABLE table_26198709_1 (original_air_date VARCHAR2, us_viewers__million_ VARCHAR2)

How many air dates does the episode with 15.50 million viewers have?
SELECT COUNT(original_air_date) FROM table_26198709_1 WHERE us_viewers__million_ = "15.50"
SELECT COUNT("original_air_date") FROM "table_26198709_1" WHERE "15.50" = "us_viewers__million_"