What average week number had the Chicago bears as the opponent?
CREATE TABLE "schedule" (
  "week" real,
  "date" text,
  "opponent" text,
  "game_site" text,
  "final_score" text,
  "record" text,
  "tv_time" text,
  "attendance" text
);
SELECT AVG("week") FROM "schedule" WHERE "opponent"='chicago bears';