XXGN
      +---------
XWHLR | XHTFJWFX
       -XWHLR
        =====
         XMPUW
        -XWHLR
         =====
          NLGQF
         -NXHJU
          =====
           QMFUX
          -WHPWJ
           =====
           XGFQW

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
missing: Y