By these calculations what is the volume of one drop of blood?

So the average amount of blood in an adult is 5000mL. There are 35 000 000 000 000 (35 trillion) red blood cells in 5000mL of blood. If there is 250 000 000 red blood cells in one drop of blood, what is the volume of one drop of blood?
Update: Also I'm pretty sure it's wrong but my first attempt was 0.00357142857142857 but I'm sure it's wrong.
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