CREATE TABLE table_20491 ("Episode" TEXT, "Broadcast date" TEXT, "Run time" TEXT, "Viewers  ( in millions ) " TEXT, "Archive" TEXT)

What was the archive for episode with 6.6 million viewers?
SELECT "Archive" FROM table_20491 WHERE "Viewers (in millions)" = '6.6'
SELECT "Archive" FROM "table_20491" WHERE "Viewers (in millions)" = '6.6'