????????
      +---------
RREJR | TETPPPWF
       -TPGMT
        =====
         JGFRP
        -UWQFU
         =====
          NPWNW
         -EPPTW
          =====
          RQJWQF
         - MJNRN
          ======
          ??????

base: 13
letters: EFGJMNPQRTUWX
difficulty: medium
missing: X