Apply the concept of differential calculus. Tofind the maxima or minima if you are only given the equation, differentiate the equation and equate to zero.
h=−16t²+96t+4
dh/dt = 0 = -32t + 96
Solving for t,
t = 3
Now, substitute t=3 to the original equation
h = -16(3)² + 96(3) + 4
h = 148 ft