????????
      +---------
FQYTP | PGQUXUPU
       -YMHEX
        =====
        FXLYHU
       -FFFXJL
        ======
         FPFXJP
        -FYXEFU
         ======
           GUMXU
          -JELLM
           =====
           ?????

base: 13
letters: EFGHJLMPQTUXY
difficulty: intermediate