????????
      +---------
PGWPN | NHLMRQUP
       -PGWPN
        =====
         JQQHQ
        -UYRXJ
         =====
          RYUNU
         -UYRXJ
          =====
          FWJXWP
         -FRYUJT
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard