A transmission diffraction grating with 600 lines/mm is used to study the line
spectrum of the light produced by a hydrogen discharge tube with the setup shown above.
The grating is 1.0 m from the source (a hole at the center of the meter stick). An observer sees the first-order red line at a distance yr = 428 mm from the hole.
Calculate the wavelength of the red line in the hydrogen spectrum.
I know the answer is 657. I want to know, if it was a reflection grating, well the answer change ?