????????
      +---------
JHFLU | FMFWUNXP
       -JHFLU
        =====
        LHYUYN
       -LTUXMN
        ======
         JFJLYX
        -JJFPGN
         ======
           WQHFP
          -UNYXY
           =====
           ?????

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