The parallelograms are similar. Find x.

[tex]\dfrac{5}{x}=\dfrac{\frac{1}{2}}{4}\\\\\\\dfrac{5}{x}=\dfrac{1}{2}\cdot\dfrac{1}{4}\\\\\\\dfrac{5}{x}=\dfrac{1}{8}\longrightarrow\boxed{x=40}[/tex]