????????
      +---------
YPGXX | HQUGJWFG
       -YPGXX
        =====
        WTLUHW
       - MQJFU
        ======
         TGNGQF
        -TQNWYW
         ======
          QLHXUG
         -NUFNTG
          ======
          ??????

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