Opponent of at boston patriots, and a Week larger than 3 had what average attendance?
CREATE TABLE "schedule" (
  "week" real,
  "date" text,
  "opponent" text,
  "result" text,
  "record" text,
  "game_site" text,
  "attendance" real
);
SELECT AVG("attendance") FROM "schedule" WHERE "opponent"='at boston patriots' AND "week">3;