Two containers $A$ and $B$ are connected by a conducting solid cylindrical rod of length $\frac{242}{7} \mathrm{cm}$ and radius $\sqrt{8.3} \mathrm{cm}.$ Thermal conductivity of the rod is $693$ watt $/\mathrm{mK}.$ The container A contains two mole of oxygen gas and the container $B$ contains four mole of helium gas. At time $t=0$ temperature difference of the containers is $50°\mathrm{C},$ after what time (in seconds) temperature difference between them will be $25°\mathrm{C}.$ Transfer of heat takes place through the rod only. Neglect radiation loss. Take $R=8.3 \mathrm{J}/\mathrm{mole} K$, $\ln 2=0.693$ and $\mathrm{\pi }=\frac{22}{7}$