An insulated vertical piston cylinder device initialy contains 10kg of water, 6 kg of which is in the vapor phase. The mass of the piston is such that it maintains a constant pressure of 200 kPa inside the cylinder. Now steam at 0.5 Mpa and 350 degrees C is allowed to enter the cylinder from a supply line until all the liquid in the cylinder has vaporized. Determine the mass of steam that has entered.