Cassette tapes cost $3 each and compact disks cost $7 each. If the number of cassette tapes was 9 more?

Question

than two times the number of compact disks, and a total of $131 was spent, how many cassette tapes and how many compact disks were purchased?

Answer 1

don't ask me why I'm doing your homework for you.. but..

8 CD's @ $7 = $56

25 cassettes @ $3 = $$75

$56 + $75 = $131

Why 25 cassettes?

Well, 8 (CD's) x 2 + 9 = 25.... all you need to to is work out how I knew to start with 8 CD's......