Light with wavelength = 0.60m falls normally on a diffraction grating inscribed on a plane surface of

Question:

Light with wavelength λ = 0.60μm falls normally on a diffraction grating inscribed on a plane surface of a piano-convex cylindrical glass lens with curvature radius R = 20cm. The period of the grating is equal to d = 6.0μm. Find the distance between the principal maxima of first order located symmetrically in the focal plane of that lens.