user: ### NOW ANSWER:
Question: what's the overall rank with rating/share 18–49 of 2.1/5
Columns: ['#', 'Episode', 'Air Date', 'Rating', 'Share', 'Rating/Share 18–49', 'Viewers (m)', 'Timeslot Rank', 'Night Rank', 'Overall Rank']
Types: ['real', 'text', 'text', 'text', 'real', 'text', 'text', 'real', 'text', 'real']
Sample row: [1.0, '"Pilot"', 'Tuesday, March 4, 2008', '8.2', 12.0, '4.5/11', '13.47', 1.0, '2', 6.0]
SQL:

assistant: SELECT COUNT("Overall Rank") FROM "Table" WHERE "Rating/Share 18–49" = '2.1/5';