C142
      +---------
821A1 | 9D373107
       -958BC
        =====
         B4CE1
        -821A1
         =====
         C71C60
        -C968B4
         ======
          16D0D7
         - D19A2
          ======
           CE888

base: 15
letters: 0123456789ABCDE
difficulty: medium