CREATE TABLE table_23242933_2 (no_in_series VARCHAR2, us_viewers__millions_ VARCHAR2)

How many different series numbers are there for the episode seen by 7.84 million people in the US?
SELECT COUNT(no_in_series) FROM table_23242933_2 WHERE us_viewers__millions_ = "7.84"
SELECT COUNT("no_in_series") FROM "table_23242933_2" WHERE "7.84" = "us_viewers__millions_"