user: ### NOW ANSWER:
Question: How many episodes had an original air date with 5.1 million viewers
Columns: ['No. in series', 'Title', 'Directed by', 'Written by', 'U.S. viewers (million)', 'Original air date', 'Production code']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'real']
Sample row: [1.0, '" Pilot "', 'Adam Bernstein', 'Tina Fey', '8.1', 'October11,2006', 101.0]
SQL:

assistant: SELECT COUNT("Original air date") FROM "Table" WHERE "U.S. viewers (million)" = '5.1';