????????
      +---------
XTJYM | UTNNGYNX
       -FJMNU
        =====
         NHWHY
        -FJMNU
         =====
         TGLQNN
        -TYNQUU
         ======
          QJPLLX
         -QQHRFT
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard