user: Question: List the number of builders where the withdrawn is 1951 and number is 42.
Columns: ['Date', 'Builder', 'Type', 'Operator', 'Number', 'Withdrawn', 'Status']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1907', 'OCC', 'combination sweeper / overhead line car', 'Saskatoon Municipal Railway', '200', '1951', 'stored']
SQL:

assistant: SELECT COUNT("Builder") FROM "Table" WHERE "Withdrawn" = '1951' AND "Number" = '42';