A1 m thick wall is made of concrete with a thermal conductivity of 1 w/m/k. there are temperature sensors on the wall's surface and buried within the wall 1 cm from each surface. one set of temperature sensors shows the surface at 30 °c and the subsurface at 32 °c, while the other shows the surface at 40 °c and the subsurface at 35 °c a. is the wall heating up or cooling down? b. what's the rate of change of thermal energy contained per unit area of wall? c. would your answer change if the wall were 0.5 m thick?