#### Answer

$m=0$

#### Work Step by Step

Through $(1,5)$ and $(-2,5)$
The slope of a line is given by $m=\dfrac{y_{2}-y_{1}}{x_{2}-x_{1}}$, where $(x_{1},y_{1})$ and $(x_{2},y_{2})$ are points through which the line passes.
Substitute the points given into the formula and evaluate:
$m=\dfrac{5-5}{-2-1}=\dfrac{0}{-3}=0$