Thank you for reporting, we will resolve it shortly
Q.
The maximum number of possible interference maxima when slit separation is equal to $4$ times the wavelength of light used in a double slit experiment is
$
d \sin \theta= n \lambda
$
$
\sin \theta=\frac{ n }{4}
$
maximum values of $\sin \theta$ can not exceed \pm 1
So possible value os $n$ is $0, \pm 1, \pm 2, \pm 3, \pm 4$ answer is 9