Which season had a season finale of May 13, 2012?
CREATE TABLE "season_ratings" (
  "season" real,
  "timeslot_edt" text,
  "season_premiere" text,
  "season_finale" text,
  "tv_season" text,
  "rank" text,
  "viewers_in_millions" real,
  "18_49_average" real
);
SELECT SUM("season") FROM "season_ratings" WHERE "season_finale"='may 13, 2012';