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.

Find a linear function L such that L(0) = 5 and L(5) = 25.