Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_68 (quantity_preserved VARCHAR, manufacturer VARCHAR, class VARCHAR)
### Question:
How many did alco -schenectady preserve of class b-3?
### Answer:
SELECT quantity_preserved FROM table_name_68 WHERE manufacturer = "alco -schenectady" AND class = "b-3"