How many different titles are there of episodes that have been seen by 7.84 million people in the US/
CREATE TABLE "table1_23242933_2" (
  "no_in_series" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_millions" text
);
SELECT COUNT("title") FROM "table1_23242933_2" WHERE "u_s_viewers_millions"='7.84';