A classroom that normally contains 40 people is to be air-conditioned with window air-conditioning units of 5- kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 kJ/h there are 10 lightbulbs in the room, each with a rating of 100 W the rate of heat transfer to the classroom through the wall and the window is estimated to be 15,000 kJ/h If the room air is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required.