(a) The volume of a growing spherical shell is V=\frac{4}{3}\pi r^3 , where the radius r is measured in micrometers ( 1 \mu m = 10^{-6} m). Find the average rate of change of V with respect to r when r changes from:

(i) 5 to 8\mu m

(ii) 5 to 6\mu m

(iii) 5 to 5.1\mu m

(i) 5 to 8

(ii) 5 to 6

(iii) 5 to 5.1

(b) Find the instantaneous rate of change of

**Please leave all your answers in terms of "pi".**

(a) (i)

(ii)

(iii)

(b)

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