Current Attempt in Progress The number of active Facebook users hit 1.55 billion at the end of September 2015 and 1.59 billion at the end of December. With t in months since the start of 2015, let f() be the number of active users in billions. Estimate f(12) and f (12) and the relative rate of change of f at t = 12. Interpret your answers in terms of Facebook users. Estimate f(12) exactly and round f (12) and the relative rate of change to four decimal places. f (12) = f' (12) = i Relative rate of change = The number of active Facebook users at the end of December 2015 was billion. The number was at billion users per month, which represents a relative rate of %% per month