From 2008 to 2011, worldwide sales of a popular smartphone brand can be modeled with an exponential function. In 2009, about 20.73 million of the smartphone brand were sold. - In 2008, about 11.63 million of the smartphone brand were sold. - In 2010, about 39.99 million of the smartphone brand were sold. If the sales continued to grow exponentially, about how many of the smartphone brand were sold in 2012