???????
      +--------
6838A | 89521B8
       -5A883
        =====
        63513B
       -6628AA
        ======
         961248
        - 8A387
         ======
         ??????

base: 12
letters: 0123456789AB
difficulty: hard
hints: 7 << 0, 0 << 4
missing: 0