????????
      +---------
JVJJY | MNMTHZLM
       -JVJJY
        =====
        GGGMYZ
       -HUWRQT
        ======
         GWNJUL
        -GNJMJL
         ======
          YGLTPM
         -YYVYPJ
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: intermediate
missing: X