For an isotropic point source of power P, intensity I at a distance $\mathrm{r}$ from it is
$$
\mathrm{I}=\frac{\mathrm{P}}{4 \pi \mathrm{r}^{2}}
$$
Since power P remains the same,
$$
\therefore \quad \frac{\mathrm{I}_{1}}{\mathrm{I}_{2}}=\left(\frac{\mathrm{r}_{2}}{\mathrm{r}_{1}}\right)^{2}=\left(\frac{9}{4}\right)^{2}
$$
$\because \quad I \propto \mathrm{A}^{2}$
where $A$ is the amplitude of a wave $\therefore \quad \frac{\mathrm{A}_{1}}{\mathrm{~A}_{2}}=\sqrt{\frac{\mathrm{I}_{1}}{\mathrm{I}_{2}}}=\frac{9}{4}$