In what Year did the Norton Team have 0 Points and 350cc Class?
CREATE TABLE "motorcycle_grand_prix_results" (
  "year" real,
  "class" text,
  "team" text,
  "points" real,
  "wins" real
);
SELECT AVG("year") FROM "motorcycle_grand_prix_results" WHERE "class"='350cc' AND "team"='norton' AND "points"<0;