1. **State the problem:** We have a tank being drained at a constant rate. After 21 minutes, it contains 371 liters, and after 31 minutes, it contains 181 liters. We want to find the relationship between time and water amount, and the initial amount of water. 2. **Identify the formula:** Since the water drains at a constant rate, the amount of water $W$ at time $t$ can be modeled by a linear equation: $$W = W_0 - rt$$ where $W_0$ is the initial amount of water, $r$ is the rate of draining (liters per minute), and $t$ is time in minutes. 3. **Calculate the rate $r$:** Using the two points $(t_1, W_1) = (21, 371)$ and $(t_2, W_2) = (31, 181)$, the rate is $$r = \frac{W_1 - W_2}{t_2 - t_1} = \frac{371 - 181}{31 - 21} = \frac{190}{10} = 19$$ So, the tank loses 19 liters per minute. 4. **Find the initial amount $W_0$:** Use the equation with one point, for example at $t=21$: $$371 = W_0 - 19 \times 21$$ Calculate: $$371 = W_0 - 399$$ Add 399 to both sides: $$371 + 399 = W_0$$ $$W_0 = 770$$ 5. **Summary:** - The amount of water decreases as time increases. - The rate of decrease is 19 liters per minute. - The initial amount of water was 770 liters. **Note:** The user suggested 752 liters, but calculation shows 770 liters based on given data.