???????
      +--------
53168 | 9388C39
       -76DC3
        =====
        C73B93
       -C18E86
        ======
         3C3AE9
        -4D4E02
         ======
         ??????

base: 15
letters: 0123456789ABCDE
difficulty: hard
attributes: fun
hints: A << 0