How many millions of viewers were there for the episode with a run time of 18:00?
CREATE TABLE "table1_1601935_1" (
  "episode" text,
  "broadcast_date" text,
  "run_time" text,
  "viewers_in_millions" text,
  "archive" text
);
SELECT "viewers_in_millions" FROM "table1_1601935_1" WHERE "run_time"='18:00';