Air Pollution The amount of nitrogen dioxide, a brown gas that impairs breathing, present in the atmosphere on a certain May day in the city of Long Beach is approximated by
$$A(t)=\frac{136}{1+0.25(t-4.5)^{2}}+28 \qquad(0 \leq t \leq 11)$$
where $A(t)$ is measured in pollutant standard index (PSI) and $t$ is measured in hours, with $t=0$ corresponding to 7 A.M. Determine the time of day when the pollution is at its highest level.