What is the total number of viewers where the share is 7 and the week rank is 64?
CREATE TABLE "u_s_standard_ratings" (
  "num" real,
  "air_date" text,
  "timeslot" text,
  "rating" text,
  "share" real,
  "18_49" text,
  "viewers" text,
  "weekly_rank" text
);
SELECT COUNT("viewers") FROM "u_s_standard_ratings" WHERE "share"=7 AND "weekly_rank"='64';