Answer
The slope m will be negative.
Work Step by Step
Consider the initial price of the car at $x=0$; here $x=0$ represents the year $2000$.
$\begin{align}
& y=mx+b \\
& =m\left( 0 \right)+b \\
& =b
\end{align}$
So, the initial price of the car is $b$.
The price of the car decreases with an increase in time.
Here, $m$ defines the slope of the graph. And, from the graph, it can be concluded that the slope defined by $m$ is negative.
Thus, the slope m will be negative.
