user: Question: What number has the builder ruston hornsby, the date 1961, and the name topsy?
Columns: ['Number', 'Name', 'Builder', 'Type', 'Works number', 'Date']
Types: ['real', 'text', 'text', 'text', 'real', 'real']
Sample row: [1.0, 'Elidir', 'Hunslet', '0-4-0 ST', 493.0, 1889.0]
SQL:

assistant: SELECT "Number" FROM "Table" WHERE "Builder" = 'ruston hornsby' AND "Date" = 1961.0 AND "Name" = 'topsy';