Answer
$m=-1$
Work Step by Step
Using $m=\dfrac{y_1-y_2}{x_1-x_2}$, the slope of the line determined by the given points, $(
3,9
) \text{ and } (
8,4
),$ is
\begin{array}{l}\require{cancel}
m=\dfrac{9-4}{3-8}
\\\\
m=\dfrac{5}{-5}
\\\\
m=-1
.\end{array}