A model for the average price of a pound of white sugar in a certain country from August $1993$ to August $2003$ is given by the function

$S(t)=-0\mathrm{.}00003237t^5+0\mathrm{.}0009037t^4-0\mathrm{.}008956t^3+0\mathrm{.}03629t^2-0\mathrm{.}04477t+0\mathrm{.}4898$

$t=$

$($cheapest$)$

$t=$

$($most expensive$)$