Someone please answer this or at least explain this to me please! PLEASE HELP!!!!

Calculate the wavelength of the laser light for a) d = 1/500 mm and b) d = 1/1000 mm. Use the modified “grating equation” given below:
nλ = d (X/L)
Remember to keep all calculations in millimeters (mm) until the end and then convert your answer to nanometers (1 nm = 10‐6mm)