How can I do this, can you explain me

Step-by-step explanation:

Start with h(t) = -16t^2 + initial height, which here is h(t) = -16t^2 + 1296.  Set this = to zero, which corresponds to the object hitting the ground (h = 0):

0 = -16t^2 + 1296.  Dividing all terms by -16, we get t^2 = 81, whose positive square root is 9.  It takes 9 seconds for the object to hit the ground.

need more information

step-by-step explanation:

the answers are in the images, i received 100% on this assignment. hope this !