For a minima at $P$, path difference of sounds reaching $P$ must be an odd multiple of half wavelength.

So, $S P-R P=(2 n+1) \frac{\lambda}{2}$

where, $n=0,1,2,3 \ldots$

From above figure,

$S P=\sqrt{(R P)^{2}+(R S)^{2}}$

$S P=\sqrt{12^{2}+5^{2}}=13$

So, path difference,

$S P-R P=13-12=1 \,m$

$Hence, from Eq. (i),$

$1=\frac{(2 n+1) v}{2 f}$

Possible values of frequency of sound are for $n=0$,

$f_{1}=\frac{v}{2}=\frac{330}{2}=165 \,Hz$

For $n=1$

$f_{2}=\frac{3 v}{2}=495 Hz , \ldots \ldots, \text { etc. }$

Hence, option $'a'$ matches with $f_{2}$.