????????
      +---------
007C0 | 18298095
       -A1E3A
        =====
        C56A20
       -C357D7
        ======
         0C34A9
        -0E0DE4
         ======
          C90D35
         -C0B26C
          ======
          ??????

base: 15
letters: 0123456789ABCDE
difficulty: hard