Test 2 Section 2 - #10 (page 455)

The key here is to recognize that these are similar triangles, so their sides are all in the same ratios.  How do we know they're similar?  Well, they both have the same angle at P (I labeled it z°), and we know angles QTP and RSP are also the same (the diagram says they're both x°). So their third angles also have to be the same (marked y° on the graph).

Since the corresponding sides of similar triangles are always in the same ratio, we know that PT/PS will be the same as QT/RS, or 8/10. 8/10 simplifies to 4/5, so our answer is (E).