What is the running time of the transmission on bbc four channels on 23 March 2008?
CREATE TABLE "transmissions" (
  "date" text,
  "time" text,
  "channel" text,
  "running_time" text,
  "notes" text
);
SELECT "running_time" FROM "transmissions" WHERE "channel"='bbc four' AND "date"='23 march 2008';