????????
      +---------
7C7B3 | C91ED6BD
       -08952
        =====
         B47D6
        -11A0E
         =====
          611CB
         -496E9
          =====
          74056D
         -730C6D
          ======
          ??????

base: 15
letters: 0123456789ABCDE
difficulty: hard