????????
      +---------
ZTRXG | TZMYZGJY
       -ZTRXG
        =====
        LGUYMG
       -LYJLXL
        ======
         PMRRWJ
        -PJZZUY
         ======
          PVNGYY
         -PHGYUU
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
missing: Q