CREATE TABLE table_name_74 (year_s__of_manufacture VARCHAR(255), quantity VARCHAR(255), axle_arrangement___uic__ VARCHAR(255))
What year was the b n2t axle arrangement, which has a quantity of 31, manufactured?
    
SQL: SELECT year_s__of_manufacture FROM table_name_74 WHERE quantity = 31 AND axle_arrangement___uic__ = "b n2t"