No link pls. The link which you are providing me is of diff question. Pls do read my query correctly.

Ques. Two wavelengths of sodium light 590 nm and 596 nm are used in turn to study the diffraction at a single slit of size 4 mm. The distance between the slit and screen is 2 m. Calculate the separation between the positions of the first maximum of the diffraction pattern obtained in the two cases. (I want to learn how 
do we assign the value of n here?- No link pls) ​