What is the total number of discs where the run time was 4 hours 40 minutes?
CREATE TABLE "dvd_releases" (
  "dvd_name" text,
  "released" text,
  "audio" text,
  "aspect_ratio" text,
  "duration" text,
  "number_of_episodes" real,
  "num_of_discs" real
);
SELECT COUNT("num_of_discs") FROM "dvd_releases" WHERE "duration"='4 hours 40 minutes';