Thermodynamics question:

Please explain your answer. Thank you

Water in an open metal drum is at a current temperature (T1=30C) at time t1. The water in the drum is to be heated from the current temperature to T2=100C at time t2 by adding steam slowly enough that all the steam condenses. The drum initially contains M1=150kg of water, and steam is supplied at Pin=4 bar and Tin=200C. How many kilograms of steam should be added so that the final temperature of the water in the tank is exactly 100C ? Neglect all heat losses from the water in this calculation. Assume that: - Specific enthalpy of the inflow: Hin^=2,860.5kJ/kg. From the steam tables in your textbook: steam at 4bar=0.4MPa pressure, and 200C. - Specific internal energy of water at time t1:U1^=125.78kJ/kg. From the saturated steam table, for saturated liquid water at 30C. - Specific internal energy at time t2:U2^=418.94kJ/kg. From the saturated steam table, for saturated liquid water at 100C