A heating system must maintain the interior of a building at 208C during a period when the outside air temperature is 58C and the heat transfer from the building through its roof and walls is 3 3 106 kJ. For this duty heat pumps are under consideration that would operate between the dwelling and (a) the ground at 158C. (b) a pond at 108C. (c) the outside air at 58C. For each case, evaluate the minimum theoretical net work input required by any such heat pump, in kJ.