Answer:
The answer is A.

Explanation:
The base price of the car is $20,000. Then, every year, the value of the car depreciates by 15%, that it means, every year the value of the car is 85% than the value of the previous year.
If we repeat the process, for example in 4 years, the value of the car will be:
20,000*0.85*0.85*0.85*0.85
You have to consider the value of the previous year to applicate the 85%.
So, the correct function to represent the car's value is:

I have attached an image that shows a graph of the correct function.