In January 2018, Trenton bought a new car for $40,000. In January 2020, he was told that the value of his car was $33,000 due to depreciation. He is told that the value of his car depreciates linearly.
1. Find a linear equation which gives the value of the car a given number of years after the year 2018.
2. In 2023, Trenton is told that he will be given $15,000 for his car if he decides to trade it in for a new car. Use the equation from part (1) above to determine the value of his car in 2023.
3. Is the $15,000 value fair based on what he was told about linear depreciation? Explain your answer?