????????
      +---------
52718 | C0964767
       -52718
        =====
        678297
       -632AAB
        ======
         7576A6
        -73C481
         ======
          785927
         -75A680
          ======
          ??????

base: 13
letters: 0123456789ABC
difficulty: challenging
hints: 5 << 0, 9 << A