A proportional relationship can be identified by the form \(y = kx\), where \(k\) is a constant and there is no y-intercept (the equation passes through the origin).
Among the given equations, the only one that fits this criterion is:
\(y = \frac{1}{3}x\)
The other equations have a constant added or subtracted to \(x\) (indicating they do not pass through the origin), and therefore do not represent proportional relationships.
So, the correct answer is:
y = \frac{1}{3}x