What is the rating of the episode with 13.47 million viewers and overall rank larger than 6?
CREATE TABLE "weekly_ratings" (
  "episode" text,
  "air_date" text,
  "rating" real,
  "share" real,
  "rating_share_18_49" text,
  "viewers_m" real,
  "timeslot_rank" real,
  "night_rank" text,
  "overall_rank" real
);
SELECT SUM("rating") FROM "weekly_ratings" WHERE "viewers_m"=13.47 AND "overall_rank">6;