Given their approximate diameters, calculate the approximate number of
a. hepatocytes (diameter 20 micrometers) radius=10 micrometers,
b. bacteria (diameter 1 micrometers) radius=0.5 micrometers, and
c. virus particles (diameter 10 nm, radius=5 nm=.005 micrometers)
that can be placed in a single layer, on the head of a pin (diameter 0.5 mm= 500 micrometers, radius=250 micrometers). Assume all of the cells, particles and the pinhead to be spherical.