Question: A pastry shop opens across the street from Haddad Library, and of course, it is very popular. The very first day, 80 people buy apple turnovers, 80 buy blueberry muffins, and 80 buy chocolate croissants; 30 buy both apple turnovers and blueberry muffins, 30 buy both apple turnovers and chocolate croissants, and 20 buy both blueberry muffins and chocolate croissants; and 20 people buy apple turnovers, blueberry muffins, and chocolate croissants. How many people bought only apple turnovers? Give justifications for your answer, once using Venn diagrams and again without using Venn diagrams.