How many losingteams were for the cup finaldate 20 August 1989?
CREATE TABLE "nsl_cup_winners" (
  "season" text,
  "cup_final_date" text,
  "winning_team" text,
  "score" text,
  "losing_team" text,
  "location" text,
  "cup_final_attendance" real
);
SELECT COUNT("losing_team") FROM "nsl_cup_winners" WHERE "cup_final_date"='20 August 1989';