A smart home contains a stand-alone device that is connected to the Internet and can either be monitored or controlled from a remote location. In 2015 there were 5 million smart homes in the United States, and by 2020 this number will increase to 25 million. Let t be years after 2015 and L, Q, and S represent different functions that model the number of smart homes during year t.

Discuss how each function models the situation. Which function is the best?