In a laboratory study of a marine invertebrate, a fertilised egg undergoes synchronous mitotic cell divisions to form a multicellular embryo.
After 222 days, the embryo has a total volume of 5.12×10−4 mm35.12 \times 10^{-4}\text{ mm}^35.12×10−4 mm3.
What is the mean volume of each cell after 222 days? Express your answer in standard form.
Show your working.