To get a perpendicular line you take the negative reciprocal of the slope, so in this case it would equal -3. Now use point-slope form to get your equation. Point slope form says that y-y1=m(x-x1) where m is your slope and x1 and y1 are the points that the graph passes through. So in this case x1=-3, y1=6, and m=-3. This gives you the equation y-6=-3(x+3). Distribute to y-6=-3x-9, and finally add 6 to both sides to get y=-3x-3
