A line perpendicular means that the slope is the negative reciprocal of the slope given. Since m=3 in the given equation, the slope in the perpendicular line has to be m = -1/3. The y-intercept can be any number.
So a line perpendicular would be y = -1/3x + b
Since you can plug anything into b, you can get many different answers. For example, y = -1/3x + 7 or y = -1/3x - 2
