????????
      +---------
WWLVM | NHMJWRVM
       -WWLVM
        =====
        MXRVHR
       -MPURXW
        ======
         ZQJVHV
        -ZPJJGU
         ======
          GTPMUM
         -GPJZYL
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: medium