????????
      +---------
GPRYF | GMRXMYXW
       -GPRYF
        =====
         XLTFY
        -XUJJM
         =====
          RNWRX
         -XUJJM
          =====
          GRFUQW
         -GXMRYJ
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
hints: R << U, F << J, X != 0
missing: H