arrow question help

Question

An arrow was shot in a parabolic path according to

        

Where a(t) is the height above the ground and t is the time in seconds.

Figure the time after the arrow is released that it  reaches  its  maximum height  above the ground in seconds 

and

Figure the maximum height of the arrow in feet  

Answer 1

Maximum height is at the vertex of the height-vs.-time parabola, which is at

t = -16/[2(-4)] sec = ? sec

Evaluate a(t) at this value of t to get maximum height.