Which Wins have a Year of 1963, and a Class of 50cc?
CREATE TABLE "motorcycle_grand_prix_results" (
  "year" real,
  "class" text,
  "team" text,
  "points" real,
  "wins" real
);
SELECT AVG("wins") FROM "motorcycle_grand_prix_results" WHERE "year"=1963 AND "class"='50cc';