HFG
       +---------
XPHFWY | GFWYFPGY
        -XPHFWY
         ======
         UXXXQPG
        -UYHRHRY
         =======
          XQURFGY
         -XYRURUY
          =======
           RWHGPY

base: 10
letters: FGHPQRUWXY
difficulty: intermediate
restrictions: no multiplication