RJWF
      +---------
XFMUF | UFXYRMMU
       -XFMUF
        =====
        MQFLXM
       -PGXQLN
        ======
         MGLRNM
        -MYRJYQ
         ======
          JFTPMU
         -JPYLWF
          ======
           JJLUY

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