Air with a mass flux of 2 kg/s enters a humidifier at 100 kPa and 20 8C

Question:

Air with a mass flux of 2 kg/s enters a humidifier at 100 kPa and 20 8C with a wet-bulb temperature of 15 8C. It leaves the humidifier at 100 kPa and 18 8C with a wet-bulb temperature of 17 8C. What is the humidity ratio at each of these states? How much water is being added per hour? Use the psychrometric chart.