CREATE TABLE "teams_with_alfa_romeo_as_an_engine_suppl" (
  "year" real,
  "entrant" text,
  "chassis" text,
  "engine" text,
  "tyres" text,
  "points" real
);

Question: What year was the brabham bt46 bt48 bt49 Chassis common?
SQL: SELECT AVG("year") FROM "teams_with_alfa_romeo_as_an_engine_suppl" WHERE "chassis"='brabham bt46 bt48 bt49';