The population of a city, P, in millions, is a function of t, the number of years since 2010, so P = f(t). What does the statement f(10) = 5 mean in terms of the population of this city?
In 2015 the population was 10 million.
In 2020 the population was 5 million.
5 years from now the population will be 10 million.
In 1915 the population was 10 million.
In 1920 the population was 5 million.