I don't understand where most of this work has come from. You have been given a detailed approach here: http://www.mathhelpforum.com/math-he...ge-159842.html

Follow it. Show all steps. Please say which step you cannot do. It sounds harsh but I do not see that you have learned anything from all my postings to your questions.

By the way, the given answer you have posted is wrong. It should be 3/y^4.