????????
      +---------
D9B2B | 7829C8E2
       -7BBAC
        =====
         10768
        -5C080
         =====
         D77A4E
        -DBD23D
         ======
          D2E192
         -DCC0A3
          ======
          ??????

base: 15
letters: 0123456789ABCDE
difficulty: challenging