Light with a wavelength of 600 nm is incident on a gemstone made of cubic zirconia (ᡦ =2.18) from air. The light makes an angle of 30° with the surface of the gem before entering it. The refracted ray makes an angle of 30° with the normal. What is the frequency of the light in the gemstone? (1 THz = 1 terahertz =10ଵଶ Hz)