What is the average year that has a final Tour position of 54 and a final Vuelta position over 55?
CREATE TABLE "grand_tour_finishers" (
  "rider" text,
  "year" real,
  "final_position_giro" real,
  "final_position_tour" real,
  "final_position_vuelta" real
);
SELECT AVG("year") FROM "grand_tour_finishers" WHERE "final_position_tour"=54 AND "final_position_vuelta">55;