Answer: Charles's law, Avogadro's law and Boyle's law.
Charles law states the constant ratio of volume to temperature, at constant pressure. Boyle's law states the constat product of pressure and volumen at constant temperature. Avogadro's law states that equal volumes of gases at the same temperature and pressure have equal number of particles.
So, all those three laws combined state the relation of pressure, volume, temperature and number of particles of a gas, which is what the ideal gas law does: PV = n RT.
