CREATE TABLE table_8808 ("Class" TEXT, "Wheel arrangement" TEXT, "Fleet number ( s ) " TEXT, "Manufacturer" TEXT, "Year made" TEXT, "Quantity made" TEXT, "Quantity preserved" TEXT)

How many did alco -schenectady preserve of class b-3?
SELECT "Quantity preserved" FROM table_8808 WHERE "Manufacturer" = 'alco -schenectady' AND "Class" = 'b-3'
SELECT "Quantity preserved" FROM "table_8808" WHERE "Class" = 'b-3' AND "Manufacturer" = 'alco -schenectady'