Bulletproof glass has layers of materials such as glass laminate, polycarbonate, and acrylic that have a nearly equal refractive index to keep the glass transparent. Bulletproof glass has a 31.75 mm thick polycarbonate layer (η = 1.581). Calculate the time taken by a light that is incident normally to the surface of the polycarbonate layer to go through the 31.75 mm thick layer.