If a ball is thrown into the air with a velocity of 40ft./s its height in feettseconds later is given by y=40t-16t^2.

a.)Find the average velocity for the time period beginning whent=2 and lasting

i.) 0.5 seconds ii.)0.1 seconds

iii.)0.05 seconds iv.)0.01 seconds

b.) Estimate the instantaneous velocity whent=2.

I am totally stuck I am not sure where to start I know. I know have to plug in the various times into the equation they gave. I also know that this problem has something to do wit-av. velocity=change in distance / change in time.