????????
      +---------
NUQQW | VZLWUQNU
       -NUQQW
        =====
        RMVVVQ
       -MYZQVV
        ======
         GWRWTN
        -GLGJHG
         ======
           WWQMU
          -YJZXL
           =====
           ?????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: medium
missing: P