Chapter 4.4, Problem 58E

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

$A\left(t\right)=\frac{136}{1+0.25{(t-4.5)}^2}+28$ (0 ≤ t ≤ 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.