????????
      +---------
1B117 | 34753CDD
       -1B117
        =====
        20048C
       -2AB30C
        ======
          7676D
         -B30BA
          =====
           0C13D
          -8A485
           =====
           ?????

base: 14
letters: 0123456789ABCD
difficulty: hard
missing: 9