QUESTION $3[15$ MARKS$]$

A $0\mathrm{.}25m^3$ cylinder is filled with ethylene gas to capacity. The safety standards require that the gas be stored at $323K$ and $11500$kPa in the industrial warehouse. As a newly hired junior engineering technologist, you have been tasked to estimate the mass of the gas in the cylinder assuming that the van der Waals equation of state can give a good approximation.