Methane gas is stored in a tank at a pressure of 15 bar and 294 K. The tank has a capacity of 0.057 m^3. Gas is allowed to escape from the tank through a partially opened valve. When the pressure in the tank has dropped to 5 bar, calculate the mass of methane removed from the tank under the following parameters:

a) If the process occurs so slowly that the temperature in the tank remains constant due to heat flow from the environment

b)If the process occurs so rapidly that negligible heat flow occurs