15. [-/3 Points] DETAILS MY NOTES If a ball is thrown vertically upward with an initial velocity of 96 ft/s, then its height after t seconds is s = 96t - 16t2. (Consider up to be the positive direction.) (a) What is the maximum height (in ft) reached by the ball? ft (b) What is the velocity (in ft/s) of the ball when it is 128 ft above the ground on its way up? ft/s What is the velocity (in ft/s) of the ball when it is 128 ft above the ground on its way down? ft/s 16. [-/4 Points] DETAILS MY NOTES The volume V of a growing spherical cell is V = x, where the radius r is measured in micrometers (1 um = 10-6 m). (a) Find the average rate of change of V with respect to / (in um /um) when / changes from 7 um to each of the following. Round your answers to one decimal place.) (i) 7 to 10 um Hm3/um (ii) 7 to 8 um um3/Hm (iii) 7 to 7.1 um um3/um (b) Find the instantaneous rate of change of V with respect to r (in um /um) when r = 7 um. (Round your answer to one decimal place.) V'(7) =[ um $/um