Answer :
the ball fall back to the ground when h(t) = -16t2 + 48t=0
-16t2 = - 48t, implies 16t = 48 so t=48/16=3
the answer is
t = 3; it takes 3 second
-16t2 = - 48t, implies 16t = 48 so t=48/16=3
the answer is
t = 3; it takes 3 second