????????
      +---------
FYYJN | PGJFGMNN
       -FYYJN
        =====
        NUPPCM
       -TYFTTC
        ======
         NFXJTN
        -NNNGYG
         ======
          UNXFNN
         -UTPJCC
          ======
          ??????

base: 12
letters: CFGJMNPTUWXY
missing: W
difficulty: intermediate