???????
      +--------
YHGQH | HXMRHXW
       -YHGQH
        =====
        YYYJPX
       -XQHTHX
        ======
         YWGRPW
        -YYUJHR
         ======
         ??????

base: 13
letters: EGHJMPQRTUWXY
difficulty: hard
missing: E