JQU
      +--------
MMLPM | WJPGYLQ
       -JJYQJ
        =====
         TNRWL
        -THLMQ
         =====
          NGFJQ
         -UNNLU
          =====
           RGLL

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