user: Question: How many writers are listed when the U.S viewers are 11.21 million?
Columns: ['No. in series', 'Title', 'Directed by', 'Written by', 'Original air date', 'U.S. viewers (millions)']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [2.0, '"In Which Sam Receives an Unexpected Visitor"', 'Tony Goldwyn', 'Mike Ostrowski', 'October3,2007', '12.30']
SQL:

assistant: SELECT COUNT("Written by") FROM "Table" WHERE "U.S. viewers (millions)" = '11.21';