????????
      +---------
WQZPN | XPMMTPRX
       -WQZPN
        =====
        ZZNGNP
       -ZJRWRJ
        ======
          GXGTR
         -LMVTT
          =====
          JRVPTX
         -JUJTQH
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
missing: Y