An apartment uses 2 kW of heating when the outside temperature is 0 degrees C and the inside temperature is 20 degrees C. When the outside temperature is -14 degrees C and the inside temperature is 22 degrees C, the heating requirement is 6 kW. The overall heat transfer coefficient U is constant and the total surface area of the apartment in contact with the outside is 50 square meters. a) What are the values: of the exchange coefficient U (W/m2-K) and of the heat generated by the people (W) present in the apartment? b) What is the minimum outside temperature at which heating is no longer necessary, if the inside temperature is kept at 20 degrees?