I'm doing review for the MAth B Regents as some of you know and there were a couple in the multiple choice section i just didn't get. Here is the link to the the answers:http://www.nysedregents.org/testing/mathre/b-key605.pdf

And here is the link to the questions:http://www.nysedregents.org/testing/mathre/b605.pdf

I just need to know the work necessary to figure out these problems. The numbers i need help in are 4,12,13,15,16, and 20. Thanks guys.