A tank of 4 m³ capacity contains 1500 kg of liquid water and vapor at 523.15 K (250 °C), the liquid water in equilibrium with its vapor, which fills the rest of the tank. A quantity of 1000 kg of water at 323.15 K (50 °C) is pumped into the tank. How much heat must be added during this process if the temperature in the tank is not to change?