Similarity of triangles is frequently used in indirect measurement. In this segment, the participants watch a demonstration of the mirror trick and see how similarity of triangles can be used to estimate Brad's height. Watch this segment after you've completed Problem B1.
Think about why in this situation having the same angle measurement is enough to make two triangles similar.
If you are using a VCR, you can find this segment on the session video approximately 11 minutes and 27 seconds after the Annenberg Media logo.