Air at a total pressure of 90 kPa, 15oC, and 75 percent relative humidity is heated and humidified to 25oC 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