What is the Winning score when the To par was −21?
CREATE TABLE "european_tour_wins_7" (
  "date" text,
  "tournament" text,
  "winning_score" text,
  "to_par" text,
  "margin_of_victory" text,
  "runner_s_up" text
);
SELECT "winning_score" FROM "european_tour_wins_7" WHERE "to_par"='−21';