????????
      +---------
41806 | 4CA51027
       -41806
        =====
         07880
        -41806
         =====
         5094A2
        -553625
         ======
          571307
         -585408
          ======
          ??????

base: 13
letters: 0123456789ABC
difficulty: hard
hints: 3 << 4
missing: B