Since another question you've asked (http://www.mathhelpforum.com/math-he...28-curves.html) strongly suggest that you're studying calculus, your trouble in solving a linear equation is surprising and of concern.
I ask again:
Can you solve for y?
What about solving for y?
If you cannot at least do this last one then I would suggest that your real problem is an insufficient grasp of the mathematical knowledge prerequisite to the topic you're currently being taught. In which case you're strongly advised to go back and revise that material in collaboration with your instructor.