2359
      +---------
979B9 | 3A2C105B
       -979B9
        =====
        C372B0
       -C9B4A8
        ======
         904115
        -9B1821
         ======
          6C3ACB
         -6614B5
          ======
           66A4C

base: 13
letters: 0123456789ABC
difficulty: medium