????????
      +---------
WMJJQ | ZPVXQUTW
       -YQPZM
        =====
        NLNPVU
       -NXQHTP
        ======
         NVPUQT
        -NPVPRW
         ======
          NULHMW
         -NTRRXZ
          ======
          ??????

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