CREATE TABLE table_24057191_2 (end_date VARCHAR2, average_viewers__millions_ VARCHAR2)

How many different end dates are there for the series seen by 4.2 million people?
SELECT COUNT(end_date) FROM table_24057191_2 WHERE average_viewers__millions_ = "4.2"
SELECT COUNT("end_date") FROM "table_24057191_2" WHERE "4.2" = "average_viewers__millions_"