A model for the US average price of a pound of white sugar from 1993 to 2003 is given by the function
$$\begin{aligned} \mathrm{S}(\mathrm{t})=&-0.00003337 \mathrm{t}^{5}+0.0009037 \mathrm{t}^{4}-0.008956 \mathrm{t}^{3} \\ &+0.0362 \mathrm{qt}^{2}-0.04458 \mathrm{t}+0.4074 \end{aligned}$$
where t is measured in years since August of $1993 .$ Estimate the times when sugar was cheapest and most expensive during the period $1993-2003 .$