When the value of something goes down over time- a house, a car, anything- it's called depreciation.
It would be expressed as exponential decay. This is because the value is going down exponentially as stated in the problem. Additionally, when it decays, the growth factor is less than one, so the value steadily decreases.
Let's rule out our other options:
B) Half-Life. This doesn't work because it's usually used for radioactive decay, which is usually a steady decrease of radioactivity and material that divides by two, hence the word half. For example:
Day 0) Started with 10 grams of plutonium Day 1) 5 grams Day 2) 2.5 grams
And so on.
C) Compound Interest. Like simple interest, but compunds usually at a certain point - yearly, monthly, every ten years, and so on. But, this is used for interest, mostly in a bank account or if you have a loan. It doesn't exhibit depreciation, and therefore it's not used to predict car value.
D) Exponential Growth- Exponential growth does not work for one main reason - it grows. That would mean that the value of the car goes up- and unless it's an old and very expensive car, that wouldn't be the case.
