????????
      +---------
UFFLP | ULQFQTJW
       -UFFLP
        =====
         WXUMT
        -UFFLP
         =====
          JGMNJ
         -UFFLP
          =====
          HWYYUW
         -HUGHQY
          ======
          ??????

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