Ok
I have the same problem, but I have overcome it. my practise tests goes from 14 to 18. I checked out the Intermediate Algreba with applications by Aufmann, 2nd edition, from school library. It is a great book. It covers almost every single problem in Topscore, and Achiever. The explanation for problems about ages, money, and travelling rates are confused in the practice tests, but in this book, that is not a problem. It shows you how to set up problems fast and accurately. You gonna love it.
I also checked on ebay, I think they have some for 20 buck, newer version
good luck