A weather balloon is inflated to a volume of 27.6 L at a pressure of 743 mmHg and a temperature of 28.1 Celsius. The balloon rises in the atmosphere to an altitude, where the pressure is 385 mmHg and the temperature is -14.9 Celsius.

Assuming the balloon can freely expand, calculate the volume of the balloon at this altitude.

What formula do I use for this problem? I looked in my book and can't find which formula to use. I know we have to convert C to K and mmHg to atm that's easy. The problem is which formula?

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