Answer:
(i)=263.9 micrometer square
(ii)=155 micrometer square
(ii)=116.9 micrometer square
(b).37.7 micrometer square
Explanation:
Given,

Average rate of change V with respect to a to b where a and b are radius

(i) 3 to 6 micrometer


micrometer square
(ii) 3 to 4



micrometer square
(iii) 3 to 3.1




micrometer square
(b) At r=3 micrometer
Instantaneous rate



micrometer square
micrometer square