The model depicts the way that a tank is being filled with water. The given estimated values are 1.2 liter/second (also the y-intercept) for the water rate and spans a time of 30 seconds. By creating a straight line with the function (t) = -1.2/30 t + 1.2. After integrating the function and solving for t = 30 seconds, we can manually calculate the value of the tank (stock) to be 18 liters.