CREATE TABLE table_24168 ("Episode" TEXT, "Broadcast date" TEXT, "Run time" TEXT, "Viewers  ( in millions ) " TEXT, "Archive" TEXT)

what is all the broadcast date when viewers were 8.4 millions
SELECT COUNT("Broadcast date") FROM table_24168 WHERE "Viewers (in millions)" = '8.4'
SELECT COUNT("Broadcast date") FROM "table_24168" WHERE "Viewers (in millions)" = '8.4'