Two diffraction gratings, A and B, are located at the same distance from the observation screens. Light

Question:

Two diffraction gratings, A and B, are located at the same distance from the observation screens. Light with the same wavelength l is used for each. The separation between adjacent principal maxima for grating A is 2.7 cm, and for grating B it is 3.2 cm. Grating A has 2000 lines per meter. How many lines per meter does grating B have?