What is the production code of the episode that had 5.43 million viewers?
CREATE TABLE "table1_24938621_3" (
  "no" real,
  "num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT "production_code" FROM "table1_24938621_3" WHERE "u_s_viewers_million"='5.43';