Answer:
[tex]CD=4 \text{ cm }[/tex]
Step-by-step explanation:
We have a similarity of triangles. Once the side BC and ED are parallel,
[tex]$\frac{BC}{AC} =\frac{ED}{AD} $[/tex]
[tex]$\frac{10}{AC} =\frac{5}{4} $[/tex]
Once [tex]AC=AD+CD \Rightarrow AC=4+CD[/tex]
[tex]$\frac{10}{4+CD} =\frac{5}{4} $[/tex]
[tex]5CD+20=40[/tex]
[tex]5CD=20[/tex]
[tex]CD=4 \text{ cm }[/tex]
