user: Question: What year was Stephenson the builder?
Columns: ['Railway', 'Builder', 'Built', 'Wheels', 'Location', 'ObjectNumber']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['SECR', 'SECR Ashford', '1901', '4-4-0', 'York', '1975-7006']
SQL:

assistant: SELECT "Built" FROM "Table" WHERE "Builder" = 'Stephenson';