(2) It is known that the world population at the end of 1999 was approximately 6 billion. Let the annual average growth rate of the population be $x\%$, and the world population at the end of 2009 be $y$ (billion). Then the functional relationship of $y$ with respect to $x$ is $y=$
(2) $60\left(1+\frac{x}{100}\right)^{10}$