For today’s Geo Quiz we were looking for the Italian city where Leonardo Da Vinci painted his famous “Last Supper.” The answer is Milan. A bit of a musical mystery has surrounded the painting for a number of years. But now Italian musical and computer expert Giovanni Maria Pala thinks he’s solved it. He’s published his work in a book called “La Musica Celata” — or “The Hidden Music.” Anchor Marco Werman speaks with him.