(a) a balloon is filled with helium (he) at an absolute pressure of 1.80 atm, a temperature of 25.0 °c, and it occupies a volume of 3.00 m^3. the balloon rises in the atmosphere to a height where the pressure is 0.500 atm and the temperature is -20 °c. 1) find the final volume of the balloon. 2) calculate the number of moles of the gas 3) calculate the internal energy of the helium gas in the balloon at the final altitude. (b) in a certain process, the temperature rises from 0.00 °c to 90 °c as 900 j of heat are extracted from 5 moles of an ideal gas. find the work done by the gas in this process. (r = 8.314 j/mk)