The temperature in degrees celsius three hours ago is 9 degrees celsius
From the question, we are told that the temperature falls at a rate of 3 degrees Celsius per hour
The current temperature is 0
The temperature an hour before is 0 + 3 = 3
The temperature an hour before the last hour is 3 + 3 = 6
And lastly the temperature before the last two will 6 + 3 = 9 degrees celsius