A human hair is approximately 40 microns (um) wide. If 1 um is equal to 10 -6 meters (m)

A human hair is approximately 40 microns (um) wide. If 1 um is equal to 10
-6 meters (m), and 1 nanometer (nm) is equal to 10-9m, then how many nanometers wide is a human hair?

A. 0.0004 nm
B. 0.004 nm
C.  4,000 nm
D. 40,000 nm