In a YDSE , 12 fringes are observed to be formed in a certain segment of screen when light of wavelength $600\; nm$ is used. If the wavelength of length is changed to $400\; nm$ , number of fringes observed in same segment of screen in given by

Question

$(a)\;12 \\ (b)\;18 \\ (c)\;24 \\ (d)\;30 $