I understand the question but not the parenthetical part.
Ignoring the part in parentheses, use (P1V1/T1) = (P2V2/T2)
note: I understand vapor pressure to be the pressure of the gas above and in equilibrium with a liquid. If gas Q has a pressure of 750 mm Hg at 287 K I don't understand how it can have a pressure of 12 mm Hg at 287 K.
It turns out that the Van Dar Waals constant b is equal to four times the total volume actually occupied by the molecules of a mole of gas. Using this figure, calculate the fraction of the volume in a container actually occupied