The process shown in figure is a constant volume electric water heater. On a particular day, as the tank temperature reached the 80C mark, the heater broke down and stopped supplying heat. At this time, water was withdrawn from this 100 liter capacity tank at the rate of 10 liter/min; cold water automatically flowed in to the tank at precisely the same rate. This exercise went on exactly for 5 min., and the water withdrawal stopped. Hence, cold water also stopped flowing in. Develop an appropriate mathematical model for this process and show that it is reasonable to consider this as a first order process and by solving the resulting differential equation model, find the final tank temperature at the end of the 5-minute period. State all your assumptions.