????????
      +---------
EDF1E | 7DE85C70
       -1EC8D
        =====
        E983FC
       -E61094
        ======
         6CE667
        -64288B
         ======
           D2460
          -F4B0F
           =====
           ?????

base: 16
letters: 0123456789ABCDEF
difficulty: medium
missing: A