Answer:
[tex]BC=8\ units[/tex]
Step-by-step explanation:
The picture of the question in the attached figure
we know that
Triangle ABC is similar to Triangle CBD by AA Similarity theorem
Remember that
If two triangles are similar, then the ratio of its corresponding sides is proportional
so
[tex]\frac{AB}{CB}=\frac{CB}{DB}[/tex]
[tex]CB^2=AB(DB)[/tex]
substitute the given values
[tex]CB^2=16(4)\\CB^2=64\\CB=8\ units[/tex]
Remember that
[tex]CB=BC[/tex]
therefore
[tex]BC=8\ units[/tex]