A frictionless piston - cylinder device contains 420 moles of ideal gas at 2 atm and 155 C. Heat is now transferred to the gas until the temperature reaches 400 C. If the piston is not attached to a shaft ( Pressure stays constant) and its mass is constant, determine the work (J) done by the gas during this process. Gas constant = 8.21x10-5 (m3.atm/K.mol)