If Light Has a Wavelength of 600 Nm in a Vacuum,what

If light has a wavelength of 600 nm in a vacuum,what is its wavelength in a material with an index of refraction of 1.50?

A) 600 nm
B) 900 nm
C) 400 nm
D) 1.35 $\times$ 10³ nm
E) 267 nm