Calculate how much money is saved per day as a result of insulating a domestic hot water tank. The tanks has a total surface area of 4.05 m². It maintains an internal temperature of 50 °C and the temperature of the room is 18 °C. The emissivity of the tank is 0.66. The Insulation is a layer or rock mineral wool of thickness 0.10 m with a surface area equal to that of the tank. The thermal conductivity of rock mineral wool is 0.032 W m⁻¹ K⁻¹. Assume the cost of electricty is 12 p per kWh.