To find the equation of the line, we first need to solve the original line for y.
-x + 3y = 9
3y = x + 9
y = 1/3x + 3
Now we know the slope of the original line to be 1/3. Since perpendicular lines have opposite and reciprocal slope, we know the new line to have a slope of -3. We can then use that along with the given point in point-slope form to find the equation.