a=-32 (acceleration is the constant g) integrating with respect to t
v=-32t+vi but initial velocity is equal to zero as it is just "dropped".
h=-32t^2/2+hi, since the initial height is 144 ft
h(t)=-16t^2+144
The object will be at the ground when h(t)=0
-16t^2+144
-16(t^2-9)=0
-16(t+3)(t-3)=0, but since we know t>0
t=3 seconds.
