please solve the question, please don't copy the answer from previous questions, it's wrong

The process shown in Figure 1 is a constant volume electric water heater. On a particular day, as the tank water 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 At this time, water was withdrawn from this 100 -liter capacity tank at the rate of 10L/min; cold water at 30C automatically flowed into the tank at precisely the same rate. This exercise went on for exactly 5 min, and the water withdrawal was stopped. (Because of the heater design, the cold water also stopped flowing in.) Develop an appropriate mathematical model for this process and show that it is reasonable to consider this a first-order process. Solve the resulting differential-equation model and find the final tank water temperature at the end of this 5-minute period. State all your assumptions