What is the winning scor of the tournament with Robin Walton as the runner-up?
CREATE TABLE "lpga_tour_20" (
  "date" text,
  "tournament" text,
  "winning_score" text,
  "margin_of_victory" text,
  "runner_s_up" text
);
SELECT "winning_score" FROM "lpga_tour_20" WHERE "runner_s_up"='robin walton';