I've seen this question in the last minutes, and I noticed that the OP has a lot of issues understanding basic (really basic) mathematics.
It's not just that the question is really bad written, or that the tittle doesn't match completely the body of the question, it's the fact that the OP seems not to understand ANYTHING about mathematics: Everyone was trying to explain him how to do a substitution, but he didn't get it, and it was very, very clear.
I wanted to comment something like "You don't have the minimal requisites for asking on this site", but I thought this might be rude and offensive (and I don't have the authority to say something like that). However, I don't think it's wrong to have such a requisites and I wondered if they actually (informally) exist.
Do they exist? Commenting something like I've said would be bad? I'm not pretending that this site should take care only of "advanced" mathematics problems, of course not, it's just that (IMHO) people who ask should have a basic level of mathematics to establish a dialogue with the people who answer.
Thanks for your time.