????????
      +---------
A7664 | B4862653
       -13665
        =====
         B8646
        -13665
         =====
          56A55
         -13665
          =====
          A8A563
         -A486A5
          ======
           ?????

base: 12
letters: 0123456789AB
missing: 0 9
difficulty: medium
hints: 0 << 9