????????
      +---------
58545 | 27B85B97
       -010159
        ======
         317589
        -341947
         ======
          04B987
         -B19521
          ======
          ??????

base: 12
letters: 0123456789AB
missing: A 6
difficulty: hard
hints: 6 << A, 8 << 7, 6 << B