????????
      +---------
B5580 | 16B478A9
       -A6037
        =====
         15078
        -A6037
         =====
          A168A
         -A6037
          =====
           B19A9
          -B5580
           =====
           ?????

base: 12
letters: 0123456789AB
missing: 2
difficulty: medium