How many Gold medals for the Nations with 6 or more Bronze medals and 18 or more Silver?
CREATE TABLE "medals_table" (
  "rank" text,
  "nation" text,
  "gold" real,
  "silver" real,
  "bronze" real,
  "total" real
);
SELECT AVG("gold") FROM "medals_table" WHERE "bronze">6 AND "silver">18;