If lines L=4x and M=x are perpendicular, what is the value of x?

Those angles are complementary, therefore, we can conclude:
[tex]\begin{gathered} 4x+x=90 \\ add_{\text{ }}like_{\text{ }}terms: \\ 5x=90 \\ Solve_{\text{ }}for_{\text{ }}x: \\ x=\frac{90}{5} \\ x=18 \end{gathered}[/tex]Answer:
x = 18