A 9 m3 tank has two sections separated by a membrane, both of which contain nitrogen gas. The nitrogen in section A has an initial density of 1.667 kg/m3 and the gas in section B has a mass of 6 kg. The membrane then breaks and the final overall density is found to be 1.778 kg/m3. Determine the initial density of the gas that existed in section B (kg/m3).