A projectile is being launched off of a platform that is 120 feet high and follows a path modeled by s(t) = -16t^2 + 56t + 120 where t represents seconds after being launched.

a. Determine the average velocity of the calculator between 1 and 3 seconds.

b. What is the instantaneous velocity of the calculator after 3 seconds.

c. When did the calculator reach its maximum height?

d. What was the projectile's instantaneous velocity as it hit the ground?