user: Question: Who wrote the episode that has a production code 3X7557?
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: [34.0, 1.0, '"Hats and Bats"', 'Christopher Chulack', 'Jonathan Lisco', 'February13,2013', '3X7551', '1.16']
SQL:

assistant: SELECT "Written by" FROM "Table" WHERE "Production code" = '3X7557';