????????
      +---------
URFQN | FLGQUJQF
       -JXUQL
        =====
        TWTQQJ
       -TNMMRQ
        ======
         TLTUXQ
        -THRHMT
         ======
          UJTNMF
         -UGTRNW
          ======
          ??????

base: 13
letters: FGHJLMNQRTUWX
difficulty: medium