????????
      +---------
PQTRU | TNQTLLLF
       -PQTRU
        =====
        XLFHHL
       -XFPLHX
        ======
         HWFMPL
        -HUQYLN
         ======
          JXUGRF
         -XFPLHX
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard