Answer:
5.51 seconds
Step-by-step explanation:
y = 0 when the stone hits the ground. At that point, t can be found from ...
... 0 = -16t^2 +486
... 0 = t^2 -30.375 . . . . divide by -16
... 30.375 = t^2 . . . . . . add the opposite of the constant
Take the square root to get ...
... √30.375 = t ≈ 5.51 . . . . seconds
