Alco -schenectady รักษาคลาส b-3 ได้กี่ตัว?
How many did alco -schenectady preserve of class b-3?
df = pd.DataFrame(columns=['quantity_preserved', 'manufacturer', 'class'])
df[(df['manufacturer'] == 'alco -schenectady') & (df['class'] == 'b-3')]['quantity_preserved']