????????
      +---------
FLTXU | QTTQGPMP
       -FLTXU
        =====
        WPRNTP
       -TQUNXH
        ======
         JYMFJM
        -YLQRTR
         ======
          XPFYMP
         -XTXPTP
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: medium