Chris you have answered the question for this person but it is highly unlikely that you have taught them anything.
You can not teach a person if you do not intereract with them.
I was about to answer when I saw you answering.
But my initial response would have been
Have you done any calculus yet?
And can you make y the subject for me (with the first expression) and then plug that y value into the second expression.
Get back to me when you have done that and we will continue furthed.
I had an extremely frustrated teacher write a comprehsive message to me recently saying that we were destryoying his teaching world by supplying full cheat answers to his students.
I could understand his frustration. This forum has become best known as a cheat site. Sad but true.