????????
      +---------
28866 | B6CD4027
       -BC5DA
        =====
         14950
        -28866
         =====
         8B6132
        -8A4C9D
         ======
          30C9D7
         -311DFC
          ======
          ??????

base: 16
letters: 0123456789ABCDEF
difficulty: challenging
hints: 2 << 7
missing: E