A balloon is filled with helium at a pressure of 2.4 x 10^5 Pa. The balloon is at a temperature of 18 degrees Celsius and has a radius of 0.25 m.
(a) How many helium atoms are contained in the balloon?
(b) Suppose we double the number of helium atoms in the balloons, keeping the pressure and the temperature fixed. By what factor does the radius of the balloon increase?