???????
      +--------
RQGPQ | JQRNGWR
       -RQGPQ
        =====
        GXHXRW
       -NMWTMW
        ======
         RPWQXR
        -YYYLUH
         ======
         ??????

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