For the tournament played on a hard surface and ending with a score of Walkover, who was the Finals opponent?
CREATE TABLE "singles_wins_5" (
  "date" text,
  "tournament" text,
  "surface" text,
  "opponent_in_the_final" text,
  "score" text
);
SELECT "opponent_in_the_final" FROM "singles_wins_5" WHERE "surface"='hard' AND "score"='walkover';