????????
      +---------
YPRJU | YGRMGFMR
       -YPRJU
        =====
         FHJYF
        -TFXMN
         =====
          JLXRM
         -QLWRW
          =====
           WXWUR
          -LTXPY
           =====
           ?????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard