????????
      +---------
TPGXW | PRNYPTNY
       -TPGXW
        =====
        RPQPJT
       -RFGWQR
        ======
         XEJRXN
        - JRYRN
         ======
          TGGNEY
         -TRJJYX
          ======
          ??????

base: 13
letters: EFGJMNPQRTWXY
difficulty: intermediate
missing: M