1. The problem statement, all variables and given/known data A balloon contains 6000m^3 of helium at 28 degrees C. and 99kPa absolute. Just before launch determine the mass of the balloon. 2. Relevant equations Determine the mass of the balloon. 3. The attempt at a solution I think you might have to use PV=mRT but im not sure about how you would get R really. Any thoughts? Is that the right equation to use here?