A cubical box of side 0.20 m is constructed from 0.012 m thick concrete panels of thermalconductivity K=0.8W m⁻¹ K⁻¹. A 100W heater is sealed inside the box and switched on. The temperature of air outside the box is 20 ◦C. After a long period of time, the air temperature inside the box will be close to​