PTWX
      +---------
EXHWG | REYEWUJF
       -RTRXY
        =====
          FUEUJ
         -FFEJF
          =====
           HTPPF
          -XRTFR
           =====
            XPTR

base: 13
letters: EFGHJLPRTUWXY
difficulty: medium
restrictions: multiplication only to find G
missing: L