user: Question: When 2/1939 is the withdrawn when was it built?
Columns: ['HR no.', 'HR name', 'CR no.', 'LMS no.', 'Built', 'Works', 'Withdrawn']
Types: ['text', 'text', 'real', 'real', 'text', 'text', 'text']
Sample row: ['70', 'River Ness', 938.0, 14756.0, '9/1915', 'Hawthorn Leslie 3095', '10/1939']
SQL:

assistant: SELECT "Built" FROM "Table" WHERE "Withdrawn" = '2/1939';