Consider a mixture of two ideal gases, X and Y, with molar masses M'_X = 10 kg/kmol and M'_Y = 20 kg/kmol, respectively, in a container. The total pressure in the container is 100 kPa, the total volume of the container is 10 m3 and the temperature of the contents of the container is 300 K. If the mass of gas-X in the container is 2 kg, then the mass of gas-Y in the container is ____ kg.
(Rounded off to one decimal place)
Assume that the universal gas constant is 8314 J kmol^-1K^-1.