What is the episode on NHK with average ratings of 9.2%?
CREATE TABLE "2008_spring_season" (
  "japanese_title" text,
  "romaji_title" text,
  "tv_station" text,
  "episodes" real,
  "average_ratings" text
);
SELECT COUNT("episodes") FROM "2008_spring_season" WHERE "tv_station"='nhk' AND "average_ratings"='9.2%';