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