7. A worker drops a hammer from a height of 784 feet. The height of the hammer, in feet, at t seconds is given by s(t)=-16t + 784. a) What is the average velocity of the hammer between 2 and 6 seconds? b) What is the instantaneous velocity of the hammer at 5 seconds? c) After how many seconds will the hammer hit the ground? d) What is the instantaneous velocity of the hammer as it hits the ground?