We know that the height h in feet of the ball after t seconds is given by the function h=-16t^2+36t+9.
f(x)=ax^2+bx+c
From the function we know that the graph is a parabola and
because of the negative lead coefficient we know that the parabola is opening down.
a.x=-b/2a=-36/(-32)=36/32=1.125 In 1.125 seconds the ball will reach its maximum height.
b. The maximum height is: f(1.125)