Solve each application.
The table shows the cost of a year's tuition, room and board, and fees at a public university from $2000-2008$. Letting $y$ represent the cost and $x$ represent the number of years since $2000,$ we find that the function defined by $$f(x)=8160(1.06)^{x}$$ models the data quite well. According to this function, when will the cost in 2000 be doubled?
$$\begin{array}{|c|c|}\hline\text { Year } & \text { Average Annual Cost } \\\hline 2000 & \$ 7,990 \\\hline 2001 & \$ 8,470 \\\hline 2002 & \$ 9,338 \\\hline 2003 & \$ 9,805 \\\hline 2004 & \$ 10,295 \\\hline 2005 & \$ 10,810 \\\hline 2006 & \$ 11,351 \\\hline 2007 & \$ 11,918 \\\hline 2008 & \$ 12,514 \\\hline\end{array}$$