Name the average year for janaprakal chandruang
CREATE TABLE "list_of_silpathorn_award_winners" (
  "year" real,
  "literature" text,
  "music" text,
  "film" text,
  "performing_arts" text
);
SELECT AVG("year") FROM "list_of_silpathorn_award_winners" WHERE "performing_arts"='janaprakal chandruang';