What is the production code of the episode before season 8, with a series number less than 31, and aired on September 21, 1995?
CREATE TABLE "season_2_1995_1996" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "directed_by" text,
  "original_air_date" text,
  "production_code" text
);
SELECT "production_code" FROM "season_2_1995_1996" WHERE "season_num"<8 AND "series_num"<31 AND "original_air_date"='september 21, 1995';