Sunlight shining in during the daytime is absorbed by the floor, interior walls, and objects in the room, raising their temperature to 37.5°C. If the house is well insulated, you may model it as losing energy by heat steadily at the rate 6 100 W on a day in July when the average exterior temperature is 4.00°C and when the conventional heating system is not used at all. During the period between 5:00 p.m. and 7:00 a.m., the temperature of the house drops and a sufficiently large “thermal mass” is required to keep it from dropping too far. The thermal mass can be a large quantity of stone (with specific heat 850 J/kg · °C) in the floor and the interior walls exposed to sunlight. What mass of stone is required if the temperature is not to drop below 18.5°C overnight?