How do I find the maximum height of this function s(t)

The height s of a ball (in feet) thrown with an initial velocity of 80 feet per second from an initial height of 8 feet is given as a function of the time t (in seconds) by

s(t) = -12t^2 + 60t + 8

1. Time where height is maximum
T=

2. Maximum height
S=

s'(t) = 0 gives
-24t + 60 = 0
t = 2.5
For this t, the second derivative s"(t) = -24 is negative. And so, s(t) is maximum for t = 2.5.
Maximum height is S = -12(2.5)^2 + 60(2.5) +8 = 233ft