Answer:
5 seconds
Step-by-step explanation:
h = -16t^2 +64t +80
We want to know when it hits the ground or when h=0
0 = -16t^2 +64t +80
Factor out -16
0 = -16 (t^2 -4t -5)
We can factor inside the parentheses
0 = -16 (t-5) (t+1)
Using the zero product property
t-5 = 0 t+1 =0
t =5 t=-1
Time cannot be negative, so t =5 seconds
