Well, if you haven't learned how to cross-multiply to solve proportions, I'm not sure how he is expecting you to proceed.
On an intuitive level, though, since you've learned how to solve linear equations, you've seen how to "clear the denominators" by multiplying through by whatever those denominators are. So what happens, in this case, if you multiply through both sides by "4" and by "4x + 1"?
Eliz.