TEXT: Choice A is correct. It's given that length WZ and length XY intersect at point Q. It follows that angle WQX and angle YQZ are vertical angles, which means they are congruent to each other. The figure shows that angle W and angle Y both have a measure of a°, so they are congruent to each other. Therefore, triangle QWX and triangle QYZ are similar triangles, where length WQ corresponds to length YQ and length WX corresponds to length YZ. Since the lengths of corresponding sides in similar triangles are proportional, it follows that YZ/YQ = WX/WQ. It's given that YQ=21, WQ=70, and WX=60. Substituting 21 for YQ, 70 for WQ, and 60 for WX in the equation YZ/YQ = WX/WQ yields YZ/21 = 60/70, or YZ/21 = 6/7. Multiplying each side of this equation by 21 yields YZ = 18 Therefore, the length of YZ is 18.
Choice A is correct. #SATPractice