What is the refractive index of the plastic?

Most plastics have refractive indices in the range from 1.3 to 1.7, but some high-refractive-index polymers can have values as high as 1.76. For infrared light refractive indices can be considerably higher. Germanium is transparent in the wavelength region from 2 to 14 µm and has a refractive index of about 4.

b. lifting dumbbell weight at 20-degree angle from the body after a 45-degree angle