user: Question: How many episodes were watched by 12.72 million U.S. viewers?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'U.S. viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: [72.0, 1.0, '"Can You Hear Me Now?"', 'David Von Ancken', 'Zachary Reiter & Pam Veasey', 'September26,2007', '12.72']
SQL:

assistant: SELECT COUNT("Written by") FROM "Table" WHERE "U.S. viewers (millions)" = '12.72';