????????
      +---------
GNLLU | NNYMXQQP
       -GNLLU
        =====
        XTTWMQ
       - LRRHU
        ======
         XPJJUQ
        -XWWWMN
         ======
          XPPRPP
         -XWWWMN
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: medium
missing: F