Answer
There were around $378.0$ million cellular phone users in the United States in 2012.
Work Step by Step
WE have to assume that the given equation would still model the number of cell phone users after 2010
2012 is 10 years after 2002 so $x=10$. Substitute 10 to $x$ in the equation to have:
$\\y=136.76(1.107)^x
\\y=136.76(1.107)^{10}
\\y=377.9508278
\\y\approx 378.0$