You want to borrow three rock CDs from your friend. She loves math puzzles and she always makes you solve one before you can borrow her stuff. Here’s the puzzle: Before you borrow three CDs, she will have 39 CDs. She will have half as many country CDs as rock CDs, and one-fourth as many soundtracks as country CDs. How many of each type of CD does she have after you borrow three rock CDs?

interesting puzzle,

total CDs=

country CDs $c$ is half of rock CDs $r$, $r=2c$

and one fourth of soundtrack $s$ as country CDs , $c=4s$

express in common variable s, $r+c+s=39$

$2(4s)+4s+s=39 \implies s=3$

so $c=12$ and $r=24$

after borrowing 3 rock CDs, there be $21$ rock CDs rest will be same

so far i think you have the right thing going for you just remember soh cah toh

step-by-step explanation:

sine over hypotenuse

cosine   equals adjacent

tangent over hypotenuse