SAT II Geometry Find the missing side length 
I'm thinking the answer is choice A but I want someone to back up my reasoning/check. So since DE and DF are perpendicular to sides AB and AC respectively that must make EDFA a rectangle. Therefore AF must be 4.5 and AE must be 7.5. Since they state AB = AC that must mean EB is 4.5 and CF is 7.5. Therefore CF rounded to the nearest whole number is 8 

Here is my thoughts on this one. It is indeed clear that triangles BED and CDF are similar. If $BD = y$ then DC is $24-y$. Using similarity we get the ratio $y/4.5 = (24-y)/7.5$ from which follows $y=9$ and so $CD=15$. With Pythagorean theorem you find 12.99 
