Given the quadratic equation:
[tex]h(t)=-16t^2+84t[/tex]The maximum point is given by the vertex of the function (h, k); where h = time the ball reaches the point, and k = maximum height. Hence:
[tex]h=\frac{-b}{2a}=\frac{-84}{2(-16)}=2.625[/tex][tex]k=-16\times(2.625)^2+84\times(2.625)=110.25[/tex]ANSWER
height = 110.25 ft