????????
      +---------
23934 | 2E07198A
       -23934
        =====
         24269
        -23934
         =====
          78328
         -3B5B9
          =====
           DEEAA
          -D0425
           =====
           ?????

base: 15
letters: 0123456789ABCDE
difficulty: hard
missing: C