????????
      +---------
WRXQM | JLVMLPGV
       -WRXQM
        =====
         GHYMP
        -VHVTZ
         =====
          PUTPG
         -HHQJL
          =====
           NPXUV
          -UPZRG
           =====
           ?????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard