????????
      +---------
NNTXN | WLMQLNQJ
       -YWUFY
        =====
        XJPYMN
       -XFJTGT
        ======
         NXFHYQ
        -NUNGUH
         ======
          XQNGFJ
         -XNRMPX
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard