By forming over 100 pinocytic vesicles per minute, a macrophage ingests over 10% of its own volume of fluid every half an hour. This is equivalent to ingesting about 100% of the macrophage's plasma membrane. If the average volume of a macrophage is about 450 µm³ and its average surface area is about 750 µm², what is the average diameter of the early pinocytic vesicles in the cell? Assume spherical vesicles. The formulas for the volume (V) and surface area (S) of a sphere of radius r are V = 4/3 × ? × r³, and S = 4 × ? × r², respectively. Write down your answer in nanometers, with no decimals, e.g. 830 nm.