Question

bacteria and other prokaryotes are found deep underground in water and in the air. one micron 10^-6 is a typical length scale associated with these microbes

Answer 1

I don't think there is enough information from the question. If you are asked to calculate the number of microbes in a certain area., then it should be that the total area or maybe the volume of that should be given so you can estimate the number of microbes. Hope this helps.