SELECT year_s__of_manufacture FROM table_name_74 WHERE quantity = 31 AND axle_arrangement___uic__ = "b n2t"
Tahun berapa pengaturan gandar B N2T, yang memiliki jumlah 31, diproduksi?
CREATE TABLE table_name_74 (year_s__of_manufacture VARCHAR, quantity VARCHAR, axle_arrangement___uic__ VARCHAR)