For this set of questions I don't need answers, per se, what I need is a little help figuring out where to begin to work them out.
1st question is: The density of air near the earth's surface is 1.29Kg/m^3. If a helium balloon with a mass of 1Kg floats in the air without rising or falling, what is the volume of the balloon? Show your working(presume that the mass of the material of the balloon is negligible).
2nd: A balloon filled with 1lt of air is 70kPa, what would be the volume of the balloon when it reaches sea level? Show your calculations.