????????
      +---------
59178 | 18780458
       -59178
        =====
        240494
       -218617
        ======
          922B5
         -44087
          =====
          040148
         -01B967
          ======
          ??????

base: 12
letters: 0123456789AB
missing: 3 A
difficulty: hard
hints: 3 << 6