????????
      +---------
57473 | C5994C2D
       -57473
        =====
         DC3EC
        -F57E6
         =====
         508632
        -E6F427
         ======
          BC4DED
         -BC7A38
          ======
          ??????

base: 16
letters: 0123456789ABCDEF
difficulty: intermediate
missing: 1