A weather balloon is inflated to a volume of $28.5 \mathrm{~L}$ at a pressure of $748 \mathrm{mmHg}$ and a temperature of $28.0^{\circ} \mathrm{C}$. The balloon rises in the atmosphere to an altitude of approximately 25,000 feet, where the pressure is $385 \mathrm{mmHg}$ and the temperature is $-15.0^{\circ} \mathrm{C}$. Assuming the balloon can freely expand, calculate the volume of the balloon at this altitude.