????????
      +---------
TTYHW | XWFPQUYH
       -TTYHW
        =====
        NLLXGU
       -NUTHJF
        ======
         WPGHXY
        -WRPNUY
         ======
          PHPURH
         -PWHTUJ
          ======
          ??????

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