????????
      +---------
02D0A | D61E56E3
       -02D0A
        =====
        39E3E6
       -B581AB
        ======
         A2672E
        -5A2346
         ======
          0BC883
         -4AA105
          ======
          ??????

base: 15
letters: 0123456789ABCDE
difficulty: medium