user: Question: Name the total number of rank timeslot for 18-49 being 3.1
Columns: ['Episode', 'First Air Date', 'Rating (18–49)', 'Share (18–49)', 'Viewers (millions)', 'Rank (timeslot)']
Types: ['real', 'text', 'text', 'real', 'text', 'text']
Sample row: [1.0, 'January 5, 2009', '3.1', 8.0, '8.74', 'N/A']
SQL:

assistant: SELECT COUNT("Rank (timeslot)") FROM "Table" WHERE "Rating (18–49)" = '3.1';