????????
      +---------
8B311 | 363976B4
       -43369
        =====
        263566
       -26B540
        ======
          B338B
         -8B311
          =====
          7B3944
         -77B3B0
          ======
          ??????

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