????????
      +---------
EXHXQ | ERRMRRMN
       -EXHXQ
        =====
         XULJR
        -EXHXQ
         =====
         JYXRJM
        -JHHTXM
         ======
          EETRNN
         -EHUYJX
          ======
          ??????

base: 13
letters: EFHJLMNQRTUXY
missing: F
difficulty: medium