????????
      +---------
ERXPU | UTMTJFPF
       -ERXPU
        =====
         HGXTF
        -FFHXT
         =====
         JEMPHP
        -JPPRME
         ======
          GPUEHF
         -GGWUTJ
          ======
          ??????

base: 13
letters: EFGHJMPQRTUWX
difficulty: hard
missing: Q