Hi I am stuck on this problem ??? I only understand (a)

Tutorial Exercise The height h (in feet) of an object falling from a tall building is given by the function h(t) = 2304 - 16t , where t is the time elapsed in seconds. (a) After how many seconds does the object strike the ground? (b) What is the average velocity of the object from t = 0 until it hits the ground? (c) Find the instantaneous velocity of the object after 1 second. Find the instantaneous velocity of the object after 2 seconds. (d) Write an expression for the velocity of the object at a general time a. (e) What is the velocity of the object at the instant it strikes the ground