An open wall consist in succession layer of fire bricks (Kf=1.21j/m²°C) a layer of lagging bricks(Kl=0.08j/m²°C) and a layer of bricks (Kb=0.6m²°C)each layer is 10cm thick, the temperature in the inside of the wall is 872°C ,on the outside 32°C. calculate the following (a)heat lost by conduction every 12 hours if the surface area of the wall is 20 m² (b) temperature in the middle of the layer of lagging bricks (c)overall heat transfer coefficient