I'm going to assume the following problem is what you meant. Let me know if not.
(x2+x-12)/(x-3) * (x2-2x-3)/(x2+5x+4)
This is a question really testing your ability to factor the polynomials involved. Once you do that it is fairly easy. Here's what it looks...
Without parentheses this expression means that the addition is done last, therefore the first thing to do is to modify the form of each of the two fractions so they each have the same denominator (bottom number). You do this by multiplying each fraction by some form of 1. ...
Can you clarify the question you are asking? I think I am missing something. Sometimes teachers need their student's help too. Can you help us understand your question better?