Someone please help me with detailed steps!

- The boy decides to ride the
TerrorTower. At its maximum height, the ride reaches 65 m above the ground. When the boy reaches the top of the tower, his gum falls out of his mouth. The height of the gum can be given by the mathematical model h(t) = 65 -4.9t^{2}, where t is the time in seconds and h is the height measured in meters.

a) Find the average velocity of the gum on the intervals 2≤t≤3 and 2≤t≤2.1

b) Find the instantaneous velocity when t = 2.