CREATE TABLE table_20490 ("Episode" TEXT, "Broadcast date" TEXT, "Run time" TEXT, "Viewers  ( in millions ) " TEXT, "Archive" TEXT)

How many millions of viewers were there for the episode with a run time of 18:00?
SELECT "Viewers (in millions)" FROM table_20490 WHERE "Run time" = '18:00'
SELECT "Viewers (in millions)" FROM "table_20490" WHERE "Run time" = '18:00'