Air at a total pressure of 90 kPa, 15C, and 75 percent relative humidity is heated and

Question:

Air at a total pressure of 90 kPa, 15°C, and 75 percent relative humidity is heated and humidified to 25°C and 75 percent relative humidity by introducing water vapor. If the mass flow rate of dry air is 4 kg/s, the rate at which steam is added to the air is
(a) 0.032 kg/s
(b) 0.013 kg/s
(c) 0.019 kg/s
(d) 0.0079 kg/s
(e) 0 kg/s