Answer
$\sqrt 10\approx3.162$ units
Work Step by Step
We know that the distance $d$ between two points $(x_{1},y_{1})$ and $x_{2},y_{2})$ is given by $d=\sqrt ((x_{2}-x_{1})^{2}+(y_{2}-y_{1})^{2})$.
Therefore, the distance between $(-9,4)$ and $(-8,1)$ will be $d=\sqrt ((-8-(-9))^{2}+(1-4)^{2})=\sqrt ((1)^{2}+(-3)^{2})=\sqrt (1+9)=\sqrt 10\approx3.162$ units