8. Consider a cubical building with sides of length 7 m. The walls are made of concrete with a thickness of 0.25 m and thermal conductivity of 0.8 W /m · °C. The temperature outside is Tout = -5 °C, while the temperature inside is Tin = 20 °C. How much energy (in joules) must the heating system provide in 12 hours to maintain the inside temperature constant? Assume heat cannot escape through the floor. In other words, assume that heat escapes through only five sides of the cube. Show your work.

8. Consider a cubical building with sides of length 7 m. The walls are made of concrete with a thickness of 0.25 m and thermal conductivity of 0.8 W /m · °C. The temperature outside is Tout = -5 °C, while the temperature inside is Tin = 20 °C. How much energy (in joules) must the heating system provide in 12 hours to maintain the inside temperature constant? Assume heat cannot escape through the floor. In other words, assume that heat escapes through only five sides of the cube. Show your work.