To find the total change in the amount of water in the tank after 6 days, we first determine how much water decreases in one day.
- The tank decreases by 10 gallons every 3 hours. There are 24 hours in a day.
- In one day, there are \( \frac{24 \text{ hours}}{3 \text{ hours}} = 8 \) intervals of 3 hours.
- Therefore, the total decrease in one day is \( 10 \text{ gallons} \times 8 = 80 \text{ gallons} \).
Now, to find the total decrease over 6 days: \[ 80 \text{ gallons/day} \times 6 \text{ days} = 480 \text{ gallons}. \]
Since the tank is decreasing in water, we express this as a negative change: \[ -480 \text{ gallons}. \]
Thus, the total change in the amount of water in the tank after 6 days is −480 gallons.