What is the average amount of points when the time (s) is 81.78?
CREATE TABLE "round_1" (
  "rider" text,
  "horse" text,
  "time_s" text,
  "faults" text,
  "total_time_s" text,
  "points" real
);
SELECT AVG("points") FROM "round_1" WHERE "time_s"='81.78';