Answer
$slope=\frac{-1}{3}$
Work Step by Step
Slope is defined as:
$\displaystyle slope=\frac{rise}{run}$
To find the slope of $DE$, we need to find the rise and run from $D$ to $E$. From the graph, we see that:
$rise=-1$ units
$run=3$ units
Thus:
$slope=\frac{-1}{3}$