????????
      +---------
PXGZM | ZRZMRYJZ
       -PXGZM
        =====
        UHWGGY
       -TQZZVL
        ======
         TTPXZJ
        - JWNHG
         ======
          XJMMGZ
         -XYVGRX
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: medium