????????
      +---------
B4AA7 | 895EC83B
       -ADCC3
        =====
        E69D98
       - ADCC3
        ======
         06B233
        -E74148
         ======
          57CC2B
         -52DBDA
          ======
          ??????

base: 15
letters: 0123456789ABCDE
difficulty: medium