user: Question: How many episodes by different writers were seen by 3.24 million people in the US?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (million)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [23.0, 1.0, '"In My Time of Dying"', 'Kim Manners', 'Eric Kripke', 'September28,2006', '3T5501', '3.93']
SQL:

assistant: SELECT COUNT("Written by") FROM "Table" WHERE "U.S. viewers (million)" = '3.24';