When was the first UK broadcast for the episode with an official TNS Gallup rating of 1575000?
CREATE TABLE "episodes_and_ratings" (
  "episode" real,
  "first_broadcast_denmark_dr1" text,
  "official_tns_gallup_ratings" real,
  "first_broadcast_uk_bbc_four" text,
  "official_barb_ratings" real
);
SELECT "first_broadcast_uk_bbc_four" FROM "episodes_and_ratings" WHERE "official_tns_gallup_ratings"=1575000;