Which year has a total of 0 points and a chassis of Toleman tg181?
CREATE TABLE "complete_formula_one_results" (
  "year" real,
  "entrant" text,
  "chassis" text,
  "engine" text,
  "points" real
);
SELECT AVG("year") FROM "complete_formula_one_results" WHERE "points"=0 AND "chassis"='toleman tg181';