If an object is dropped from a height of 144 ft, the function h(t) = –16t² + 144 gives the height of the object after t seconds. when will the object hit the ground?

When the object hits the ground, the value of h(t) of the given function becomes 0 such that,
                                 0 = -16t² + 144      or 144 - 16t² = 0
The equation above becomes a difference of two squares where 144 is the square of 12 and 16t² if the square of 4t. Factoring then gives,
                                    (12 - 4t) x (12 + 4t) = 0
                           12 - 4t = 0 ; t = 3       and 12 + 4t = 0   ; t = -3
The answer is 3 seconds.