If a ball is thrown straight up into the air with an initial velocity of [math] ft/s, its height in feet after [math] second is given by [math]. Find the average velocity for the time period beginning when [math] and lasting
(i) [math] seconds

(ii) [math] seconds

(iii) [math] seconds

Finally based on the above results, guess what the instantaneous velocity of the ball is when [math].