????????
      +---------
8D445 | 7B72A692
       -8D445
        =====
        AB1416
       - 4D2CD
        ======
         E03299
        -EED566
         ======
          8A9AA2
         -83D30A
          ======
          ??????

base: 15
letters: 0123456789ABCDE
difficulty: medium