user: Question: What is the lowest quantity of the 1B n2 type, which was retired in 1907-12?
Columns: ['Class', 'Quantity', 'Type', 'Delivered', 'K.B.Sts.B. Class', 'Retired']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['A', 24.0, '2A n2', '1857-59', 'B IX*', '1902-08']
SQL:

assistant: SELECT MIN("Quantity") FROM "Table" WHERE "Type" = '1B n2' AND "Retired" = '1907-12';