????????
      +---------
XNMYH | HXWJWTRU
       -XNMYH
        =====
         YHPMT
        -XNMYH
         =====
         XFYYWR
        -XYGHXL
         ======
           FXUMU
          -YRJMF
           =====
           ?????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
missing: Q