user: Question: How many did Alco -Schenectady preserve of class B-3?
Columns: ['Class', 'Wheel arrangement', 'Fleet number(s)', 'Manufacturer', 'Year made', 'Quantity made', 'Quantity preserved']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['0-6-0 — OOO', '0-6-0 — OOO', '0-6-0 — OOO', '0-6-0 — OOO', '0-6-0 — OOO', '0-6-0 — OOO', '0-6-0 — OOO']
SQL:

assistant: SELECT "Quantity preserved" FROM "Table" WHERE "Manufacturer" = 'Alco -Schenectady' AND "Class" = 'B-3';