a b c d

d

$\text{Let length of the screen on which fringes are obtained is L}$ $\text{Then fringe width is } \beta = \frac{L}{92} = \frac{\lambda D}{d}$ $\text{Let new wavelength is }\lambda' \text{and number of fringes are n}$ $Then \frac{\lambda D}{d} = \frac{L}{n}$ $\Rightarrow n = \frac{92\times \lambda}{\lambda'} = 99$