Step 1 :Given the line equation in the form $ax + by = c$, where $a = 3$ and $b = -9$.
Step 2 :The slope of a line in this form is given by $-a/b$. So, the slope of the given line is $-3/-9 = 1/3$.
Step 3 :A line parallel to the given line will have the same slope. Therefore, the slope of a line parallel to the given line is also $1/3$.
Step 4 :A line perpendicular to the given line will have a slope that is the negative reciprocal of the given line's slope. Therefore, the slope of a line perpendicular to the given line is $-1/(1/3) = -3$.
Step 5 :Final Answer: The slope of a line parallel to the given line is \(\boxed{\frac{1}{3}}\) and the slope of a line perpendicular to the given line is \(\boxed{-3}\).