An LPG or liquefied petroleum gas is made up of a mixture of propane (C₃H₈) and butane (C₄H₁₀). Assume that the mole fractions of propane and butane in a certain LPG mixture are 0.822 and 0.178, respectively. A 36.5 g sample of an LPG mixture has a volume of 10.0 L at 15.0°C. Calculate the pressure (in atm) of the mixture.