CREATE TABLE table_2391 ("Episode" FLOAT, "First Air Date" TEXT, "Rating  ( 18\\u201349 ) " TEXT, "Share  ( 18\\u201349 ) " FLOAT, "Viewers  ( millions ) " TEXT, "Rank  ( timeslot ) " TEXT)

Name the total number of rank timeslot for 18-49 being 3.1
SELECT COUNT("Rank (timeslot)") FROM table_2391 WHERE "Rating (18\u201349)" = '3.1'
SELECT COUNT("Rank (timeslot)") FROM "table_2391" WHERE "Rating (18\u201349)" = '3.1'