FXR
      +--------
PQLJW | GRPJNWP
       -JRHPT
        =====
        UWNPWW
       -UTUXWJ
        ======
         UQTMRP
        -UYXLPQ
         ======
          FXNMJ

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