user: Question: Which Built at has a Date of 1946, and a 1947 Nos of 3556/7?
Columns: ['1946 Nos', '1947 Nos', 'Date', 'Built at', 'LMS Nos', 'BR Nos']
Types: ['text', 'text', 'real', 'text', 'text', 'text']
Sample row: ['3100-24', '3500-24', 1944.0, 'Brighton', '8705-29', '48705-29']
SQL:

assistant: SELECT "Built at" FROM "Table" WHERE "Date" = 1946.0 AND "1947 Nos" = '3556/7';