Question 871637
h= -16t^2+64t+4
using the derivative for the vertex
-32t+64=0
h= -16*2^2+64*2+4
h=-16*4+64*2+4
h=-64+128+4
h=68
t=2 h=68
or using -b/2a for the vertex

t=-64/-32=2
h=68 from above

(2,68) 
At 2 seconds it reaches 68 feet.