1. **State the problem:** We have a car initially worth 20000 dollars that depreciates by 4000 dollars each year. 2. **Write the formula:** The value of the car after $x$ years is given by $$y = 20000 - 4000x$$ where $y$ is the value in dollars and $x$ is the number of years. 3. **Use the formula to find when the car's value is 4000 dollars:** Set $y = 4000$ and solve for $x$: $$4000 = 20000 - 4000x$$ 4. **Solve the equation:** Subtract 20000 from both sides: $$4000 - 20000 = -4000x$$ $$-16000 = -4000x$$ Divide both sides by -4000: $$x = \frac{-16000}{-4000} = 4$$ 5. **Interpretation:** After 4 years, the car's value will be 4000 dollars. **Final answer:** After $4$ years, the car's value will be $4000$.