The equation of motion is s(t) = -16t2 + 49t +53.9.
If there is anything solid left of the material (embers will float and there is no way to predict when they will hit ground), it will hit ground when s(t)=0,
Maximum height will be attained when 32t=49.
This is true because the maximum height of a parabola will occur when t=-b/2a where
the parabola is given by ax2+bx+c=f(x). In order to show this by algebra you need to convert the equation to vertex form.