????????
      +---------
81696 | 1485877B
       -81696
        =====
        835157
       -8384A3
        ======
          2BB77
         -9B863
          =====
          83A27B
         -8384A3
          ======
          ??????

base: 12
letters: 0123456789AB
difficulty: medium
missing: 0