Let's begin by listing out the given information
The slope of a line is 5
[tex]m(line)=5[/tex]For a perpendicular line, the slope is given by:
[tex]\begin{gathered} m(perpendicular)=-\frac{1}{m(line)} \\ m(line)=5 \\ m(perpendicular)=-\frac{1}{5} \end{gathered}[/tex]