What is the sum of Points for 250cc class, ranked 13th, later than 1955?
CREATE TABLE "motorcycle_grand_prix_results" (
  "year" real,
  "class" text,
  "team" text,
  "points" real,
  "rank" text,
  "wins" real
);
SELECT SUM("points") FROM "motorcycle_grand_prix_results" WHERE "class"='250cc' AND "rank"='13th' AND "year">1955;