user: Question: What is the date of the poll with Silbert at 18%?
Columns: ['Source', 'Date', 'Goldberg', 'Murray', 'Silbert', 'Undecided']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Suffolk University', 'September 15–17, 2006', '35%', '22%', '21%', '31%']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Silbert" = '18%';