What is the average year of Maja Pohar's Women's singles matches?
CREATE TABLE "previous_winners" (
  "year" real,
  "men_s_singles" text,
  "women_s_singles" text,
  "men_s_doubles" text,
  "women_s_doubles" text,
  "mixed_doubles" text
);
SELECT AVG("year") FROM "previous_winners" WHERE "women_s_singles"='maja pohar';