When Brendan kicks a football, its height in feet can be modeled by the equation h=−16t2+85t

where t is the time, in seconds, after Brendan kicks the ball. What is the maximum height and what time does it reach this height?

The time constant is calculated using the following rule:
T = RC 
where:
R is the value of the resistance = 600 ohm
C is the value of the capacitor = 0.01 * 10^-6 Farrad

Substitute with the givens ti get the time constant as follows:
T = 600 * 0.01 * 10^-6
T = 6 * 10^-6 seconds = 6 microseconds