physics help-the central and first-order principal maxima are separated by 0.488 m on a wall 1.74 m from the g?

The distance between grating lines d = 1 / 5305 /cm = 0.0001885 cm = 0.001885 mm = 1.885 μm.
We need the angle between the central and 1st order principal maxima θ. The separation x = 0.488 m and the distance between grating L = 1.74 m, so tan θ = x/L = 0.488 m / 1.74 m = 0.2805 or θ = 15.7°. We now apply the equation for diffraction grating maxima d x sin θ = mλ, m = order = 1, so: λ = 1.885 nm x sin 15.7° = 0.51 μm = 510 nm (green light).