user: Question: Which class at 55 built?
Columns: ['Class', 'Wheels', 'Date', 'No. built', 'Loco Nos.', 'Comments']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['D3', '0-4-4T', '1892-6', 36.0, '363-398', '396 and 397 rebuilt as Class D3X in 1909']
SQL:

assistant: SELECT "Class" FROM "Table" WHERE "No. built" = 55.0;