What does it mean for a line to be parallel? Work through it.
First, get that in standard form:
y = 3x - 5
Do you see that 3 is the SLOPE (y = mx + b) and -5 is the y-intersect?
Thus, what is a parallel line? Do you agree a parallel line has to have the same slope, and thus y = 3x + c is a parallel line? Since it has to pass through the origin, y = 3x is your answer (essentially, y = 3x + 0).