How many air dates had 3.2 million viewers?
CREATE TABLE "table1_26448179_4" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real,
  "u_s_viewers_millions" text
);
SELECT COUNT("original_air_date") FROM "table1_26448179_4" WHERE "u_s_viewers_millions"='3.2';