????????
      +---------
PGQLR | UGLTRXUF
       -PGQLR
        =====
        HNNXNX
       - LFUMG
        ======
         TTNUYU
        -TJWLPX
         ======
           QQTRF
          -PGQLR
           =====
           ?????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard