????????
      +---------
TGGUP | GXWFXWAA
       -TGGUP
        =====
        FRXUPW
       -FMPTFX
        ======
         FTXRGA
        -FMPTFX
         ======
          WTAPRA
         -WUTXWF
          ======
          ??????

base: 10
letters: AFGMPRTUWX
difficulty: hard