Need help practice problem

Q2) A balloon, with a diameter of 60 cm, filled with 2 moles of Helium at sea level at 200C. Molar weight of Helium is 4g/mole. a) Calculate the pressure inside the balloon. b) Calculate the mass of the helium gas inside the balloon. c) Calculate the rms speed (Vrms) of the helium molecules inside the balloon. d) If the balloon escapes a child's hand, what is the radius of the balloon when it reaches an altitude at which the temperature is (10.0)C and the pressure is only 0.5 atm (assuming no leak)