4 The number of monthly active Facebook users worldwide in millions between the year 2009 and the year 2017 can be modeled approximately by the function f t 2 12x 27 43x 301 48x 180 4 where t is time in years since 2009 Use the graph of this model to determine in the middle of what year the number of monthly active Facebook users reached 1 000 000 000 A Middle of 2011 B Middle of 2012 C Middle of 2013 D Middle of 2014 E Middle of 2015