Tell me the total number of date for carpet
CREATE TABLE "open_era_singles_finals_3_2" (
  "outcome" text,
  "date" real,
  "championship" text,
  "surface" text,
  "opponent_in_the_final" text,
  "score_in_the_final" text
);
SELECT COUNT("date") FROM "open_era_singles_finals_3_2" WHERE "surface"='carpet';