????????
      +---------
05459 | 52030BAB
       -393A1
        =====
         5529B
        -393A1
         =====
         B2370A
        - 829B0
         ======
          0A32BB
         -0BAB72
          ======
          ??????

base: 12
letters: 0123456789AB
difficulty: hard
missing: 6