Answer
slope is undefined
Work Step by Step
RECALL:
The slope $m$ of a line is given by the formula $m=\dfrac{y_2-y_1}{x_2-x_1}$ where $(x_1, y_1)$ and $(x_2, y_2)$ are points on the line.
Find the slope of the line that contains the two given points using the formula above to obtain:
$m=\dfrac{-8-7}{4-4}=\dfrac{-15}{0}\space \text{slope is undefined}$