Read the passage below and solve the questions based on it.
In the figure given above, each hexagon is regular and has side measuring ‘a’ cm. it is also given that the last row has ‘n’ such regular hexagons and all the hexagons are inscribed by circles.
Suppose the above figure is a 3-D figure and each hexagon is inscribed by a sphere of maximum volume. The height of the hexagonal figure is just enough to contain the sphere, then find the volume of the shaded region (there are ‘n’ hexagonal figures of side ‘a’ in the last row).