What is the Tournament with a Margin of victory that was 4 strokes?
CREATE TABLE "pga_tour_wins_21" (
  "date" text,
  "tournament" text,
  "winning_score" text,
  "to_par" text,
  "margin_of_victory" text
);
SELECT "tournament" FROM "pga_tour_wins_21" WHERE "margin_of_victory"='4 strokes';