9514 1404 393
Answer:
5.25 seconds
Step-by-step explanation:
The vertex of the parabola defined by ax²+bx+c is located at x = -b/(2a).
The time to maximum altitude is ...
x = -(168)/(2(-16)) = 168/32 = 5.25
The time at which maximum height is reached is 5.25 seconds after launch.