????????
      +---------
8B9DE | D79963B5
       -76198
        =====
        A32C73
       -A7EB3D
        ======
         A9062B
        -AEDA2E
         ======
           1DC85
          -94CBD
           =====
           ?????

base: 15
letters: 0123456789ABCDE
difficulty: medium