A cavity wall is made of bricks 0.1m thick with an air space 0.1m thick between them. Assuming the thermal conductivity of brick is 20 times that of air, calculate (i) The thickness of brick which conducts the same quantity of heat per second per unit area as 0.1m of air. (ii) If the thermal conductivity of brick is 0.5 Wm-1K-1, calculate the rate of heat conducted per unit area through the cavity wall when the outside surfaces of the brick walls are respectively 19°C and 4°C.