What was the original air date for the episode with 3.90 u.s. viewers (millions)?
CREATE TABLE "table1_12722302_2" (
  "no" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "bens_location" text,
  "original_air_date" text,
  "u_s_viewers_million" text
);
SELECT "original_air_date" FROM "table1_12722302_2" WHERE "u_s_viewers_million"='3.90';