????????
      ----------
HUFHW ) PPFMHXNG
       -GFFNR
        =====
         FJHPX
        -MXXJN
         =====
          YFGWN
         -YTFLY
          =====
           XMJWG
          -PLPMF
           =====
           ?????

base: 15
symbols: FGHJLMNPQRTUWXY
difficulty: hard
hints: U << Y
missing: Q