Check the picture below.
thus is at 0 = -16t² + 96t +640,

well, clearly it can't be a negative value for the elapsed seconds, so it can't be -4.
A perpendicular bisector literally bisect the perpendicular intersection in half the angle bisector is half of the angle. for example a 90 degree angle split in half is 45 degrees on both sides
I don't think that anybody in Elementary School would Understand this you might want to post this question in the High School section.
Hope it gets answered :)
Answer:
Step-by-step explanation:
(x,y)=(4,-1/2)