A 2m^3 rigid tank contains compressed methane whose density is 15.25 kg/m^3. A valve holds the compressed methane inside the tank until it is needed for an industrial burner. While working in the fuel storage area, a maintenance man mistakenly hits the valve connected to the methane tank causing it to break off the tank. All the methane in the tank escapes into the room until the density in the tank decreases to its STP value of 0.717 kg/m^3. Determine the mass of air that has escaped to the room from the tank. Assume that the flow of methane is one directional and there is no air in the tank when STP density is reached.