d
We know
$\mathrm{v}_{\mathrm{rms}}=1.085 \mathrm{v}_{\mathrm{avg}}$
$\Rightarrow \sqrt{\frac{3 P}{\rho}}=1.085 \mathrm{v}_{\mathrm{avg}} ; \rho$ is density
In this case $\rho$ is constant
$\therefore P \propto\left(V_{\text {avg }}\right)^{2}$
$\therefore \frac{P_{f}}{P_{i}}=\left[\frac{\left(v_{\text {avg }}\right)_{f}}{\left(v_{\text {avg }}\right)_{i}}\right]^{2}=4$