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

(a) Find the average velocity for the time period beginning with $t=2$ and
(1) lasting 0.5 seconds: ft/s
(2) lasting 0.1 seconds: ft/s
(3) lasting 0.05 seconds: ft/s
(4) lasting 0.01 seconds: ft/s

(b) Find the instantaneous velocity when $t=2$: ft/s