Here is a sketch of the situation.
The distance covered by the mouse is the red line and its magnitude is
[tex]\sqrt[]{8^2+5^2}=\sqrt[]{89}\approx9.43[/tex]
The direction if the red line is
[tex]\theta=\tan ^{-1}(\frac{8m}{5m})[/tex][tex]\theta=57.995^o[/tex]
This angle is directed to the left.
