????????
      +---------
1A7B0 | 49A6A94B
       -1A7B0
        =====
        B25219
       -BA9621
        ======
          39744
         -0335B
          =====
          68367B
         - 20809
          ======
          ??????

base: 12
letters: 0123456789AB
difficulty: medium