????????
      +---------
7B82B | 8810B710
       -7B82B
        =====
        641807
       -6B67B0
        ======
         6A2A71
        -6B67B0
         ======
          318910
         -325A9B
          ======
          ??????

base: 12
letters: 0123456789AB
difficulty: medium