????????
      +---------
HMTPW | GFQRJNHP
       -XPHMQ
        =====
        YNJXRN
       -YNXWTT
        ======
          LQJRH
         -HMTPW
          =====
          TGPTJP
         -TFMJNL
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
missing: U