We definex as a year between 2008 and 2013 and y as the total number of smartphones sold that year, in
millions. The table shows values ofx and corresponding y values.

2008 - 3.7
2009 - 17.3
2010 - 42.4
2011 - 90
2012 - 125
2013 - 153.2

Is y a function of x? Explain why or why not.