????????
      +---------
GTHMW | GYNLYXRL
       -GTHMW
        =====
         MMFXX
        -MQTXL
         =====
          JPNUR
         -GTHMW
          =====
          GFMYFL
         -GWYYPT
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard