We need to identify the correct rule to solve this problem.
Notice that triangles EGF and GHF are similar:
So, we have:
[tex]\begin{gathered} \frac{EF}{GF}=\frac{GF}{HF} \\ \\ \frac{10}{5}=\frac{5}{x} \end{gathered}[/tex]
Now, using the leg rule, we obtain:
