A diffraction grating is made up of slits of width 300 nm

Question

Solve the all parts of given problem:

Problem: A diffraction grating is made up of slits of width 300 nm with separation 620 nm. The grating is illuminated by monochromatic plane waves of wavelength = 450 nm at normal incidence.

Part A: How many maxima are there in the full diffraction pattern?

Part B: What is the angular width of a spectral line observed in the first order if the grating has 1500 slits?

I want help to find how many maxima are there in the full diffraction pattern.