Air pollution the level of ozone an invisible gas that

Question

Question: Air pollution the level of ozone, an invisible gas that irritates and impairs breathing, present in the atmosphere on a certain may day in the city of riverside was approximated by

A(t)  = 1.0974t³ - 0.0915t⁴             (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. Use the second derivative test to show that the function a has a relative maximum at approximately t = 9. Interpret your results.