Triangle ABC is similar to try to go to a DE what is the length of Ec

So, as both triangles are similar, we can write the following equation:
[tex]\frac{16}{4}=\frac{5+x}{5}[/tex]Now, all we need to do is to solve this equation for x:
[tex]\begin{gathered} 80=4(5+x) \\ 20=5+x \\ x=15 \end{gathered}[/tex]Thus, x=15.