?????????
      +----------
BCE69 | 3D55BA806
       -BCE69
        =====
        56D91A
       -5DC136
        ======
         563AC8
        -5DC136
         ======
          58D800
         -58F7A7
          ======
            A12B6
           -8DC77
            =====
            ?????

base: 16
letters: 0123456789ABCDEF
difficulty: medium
missing: 4