(a) The volume V of a growing spherical cell is
V = 4/3pr3,
where the radius is measured in micrometers (1 µm = 10-6m). Find the average rate of change of V with respect to r when r changes from 3 to each of the following. (Round your answers to one decimal place.)
(i) 3 to 6 µm
µm3/µm

(ii) 3 to 4 µm
µm3/µm

(iii) 3 to 3.1 µm
µm3/µm

(b) Find the instantaneous rate of change of V with respect to r when r = 3 µm. (Round your answer to one decimal place.)
V'(3) = µm3 / µm