user: Question: How many episodes  of 30 minutes were written by John Sullivan?
Columns: ['Episode', 'Original title', 'Directed by', 'Written by', 'Original airdate', 'Duration', 'Viewership']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [8.0, '" Testing Times "', 'Dewi Humphreys', 'Jim Sullivan', '15September2006', '30 minutes', '5.04 million']
SQL:

assistant: SELECT COUNT("Duration") FROM "Table" WHERE "Written by" = 'John Sullivan';