What is the pa listed when the ends won is 21?
CREATE TABLE "standings_pool_b" (
  "skip_club" text,
  "w" real,
  "l" real,
  "pf" real,
  "pa" real,
  "ends_won" real,
  "ends_lost" real,
  "blank_ends" real,
  "stolen_ends" real
);
SELECT MAX("pa") FROM "standings_pool_b" WHERE "ends_won"=21;