A cubical container full of hot water at a temperature of 90 °C is completely lagged with an insulating material of thermal conductivity 6.4 X 10-² Wm-¹K-1. The edges of the container are 1.0 m long and thickness of the lagging is 1.0 cm. Estimate the rate of flow of heat through the lagging if the external temperature of the lagging is 40 °C. Discuss qualitatively how your results will be affected if the thickness of the lagging is increased considerably, if the temperature of the surrounding air is 18 °C. (7)