How old is the mother?

      Professor Layton is one of my favorite Nintendo DS game. In this game include many puzzle solve and reveal mystery in a story together.  The main character is Hershel Layton, a professor of archeologist , who prides himself on gentlemanly conduct and puzzle mastery. He is always followed by his  apprentice, the young Luke Triton, who also practise at solving puzzles. 


So this one is a puzzle I choose. Of course I've already known an answer but i just want to share it to you guys! Can you solve it?