What was the margin of victory in the tournament with a winning score of −3 (74-68-72-71=285)?
CREATE TABLE "pga_tour_wins_6" (
  "date" text,
  "tournament" text,
  "winning_score" text,
  "margin_of_victory" text,
  "runner_s_up" text
);
SELECT "margin_of_victory" FROM "pga_tour_wins_6" WHERE "winning_score"='−3 (74-68-72-71=285)';