????????
      +---------
999CD | 2CD30760
       -22706
        =====
         B5577
        -00A60
         =====
          A0AC6
         -8A449
          =====
           D0470
          -BD192
           =====
           ?????

base: 14
letters: 0123456789ABCD
difficulty: challenging
hints: 7 << C