F91D
      +---------
FDD22 | C558D6F1
       -FDD22
        =====
         55E66
        -6DEDE
         =====
         F5D65F
        -F6D3AE
         ======
          FD0C91
         -FBD2D7
          ======
           F05A6

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