A helium-filled balloon has a volume of 4.50 L when the temperature is 22.5 degrees C and the barometric pressure is 747.3 mmHg. The balloon’s volume is neither increasing nor decreasing, so what is the pressure of the helium inside the balloon? I feel like there's either not enough information here to solve or the answer is simply 747.3 mmHg, but I'm not sure at all. Any help would be much appreciated.