The height of a free falling object at time t can be found using the function, h(t) = - 12t2 + 36t. Where h(t) is the height in feet and t is the in seconds. Find the time when the object hits the ground

For this case we have the following equation:
 h (t) = - 12t2 + 36t
 When the object hits the ground we have:
 - 12t2 + 36t = 0
 We look for the roots of the polynomial:
 t1 = 0
 t2 = 3
 Therefore, the time it takes the object to hit the ground is:
 t = 3 s
 Answer:
 the time when the object hits the ground is:
 t = 3 s