????????
      +---------
WPHXT | RPLQFJXR
       -WPHXT
        =====
        UNUMLJ
       - MJTJL
        ======
         UPMMWX
        -URQTYH
         ======
          UHMXTR
         -UQYHWX
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: medium
missing: G