C650
      +---------
38611 | 31C53888
       -38611
        =====
         564C88
        -0A1084
         ======
          A1A3A8
         -A05A23
          ======
           81AC2

base: 13
letters: 0123456789ABC
hints: 9 << 2, 7 + 7 = 4
difficulty: medium
missing: 9 B 7