A balloon has a volume of 1.0 m3. As it rises in the Earth's atmosphere, its volume expands. What will be its new volume if its original temperature and pressure are 20eC and 1.0 atm, and its final temperature and pressure are -40e C and 0.10 atm?

The zeroth law of thermodynamics:  If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.

Boyle's law: The volume of a gas is inversely proportional to the absolute pressure applied to it when the temperature is kept constant.
Charles's law: The volume of a given amount of gas is directly proportional to the absolute temperature when the pressure is kept constant.
Gay-Lassac's law: At constant volume, the absolute pressure of a gas is directly proportional to the absolute temperature.