AT&T Inc., the large U.S. phone company and the one-time monopoly, left the payphone business at the beginning of 2009 because people were switching to wireless phones. U.S. consumers owning cellphones reached 80% by 2007 and 95% by 2018 according to the Pew Research Center. Consequently, the number of payphones fell from 2.6 million at the peak in 1998 to only about 100,000 in 2018 (money. cnn.com/2018/03/19/news/companies/payphones/  index.html). Use graphs to explain why a monopoly may exit a market when its demand curve shifts to the left.