1)
The vertex of the graph is (1,3).
2)
The vertex of the graph is a maximum.
3)
h=0
Then:
-16t²+45t+6=0
we need solve this square equation:
t=[-45⁺₋√(2025+384)] / -32=(-45⁺₋49.08) / -32
We have two solutions:
t₁=(-45+49.08)/-32=2.94 s≈3 s
t₂(-45+49.08)/-32=-0.15 this solution is not valid.
Answer: 3 s.