I found your complete question in another source. See attached image. For this case what you should see is that you have two similar triangles. We then have the following relationship: ((AB) / (BX)) = ((CD) / (DX)) We cleared CD: CD = ((AB) / (BX)) * (DX) Substituting the values: CD = ((12) / (5)) * (2.5) CD = 6 Answer: CD = 6
