????????
      +---------
68521 | 45268913
       -B6A977
        ======
         08B1A1
        -820894
         ======
          B10073
         -B54984
          ======
          ??????

base: 12
letters: 0123456789AB
difficulty: medium
hints: 0 << 9, 0 << A, 2 << 3