monochromatic light with the wavelength ? falls on the diffraction grating with the grating constant d=6? . at what angle will the third diffraction maximum be observed?

please let me know the wavelength. if wavelength is known then we can use 
d*sin theta = n lambda
where d = 6 , n =1 and value of lambda
and we can calculate the angle theta
Thanks & Regards.
Nirmal Singh
Askiitians Faculty

hello :) the question like this , i need all the levels that solve it monochromatic light with the wavelength ? falls on the diffraction grating with the grating constant d=6? . at what angle will the third diffraction maximum be observed?