????????
      +---------
B047A | 2A4A9AD3
       -B047A
        =====
        BC1E6A
       - 18B17
        ======
         BD866D
        -BD0EE5
         ======
           3BC63
          -246D1
           =====
           ?????

base: 15
letters: 0123456789ABCDE
difficulty: hard