As it is perpendicular to y = -3x + 2 and the gradient of that is -3 we know that the gradient of our line must be -1 / -3 = 1/3.
Now we have the general equation of a line m = (y-y1)/(x-x1) to which we can substitute our values.
1/3 = (y - 1)/(x - 3)
x - 3 = 3 * (y - 1)
x - 3 = 3y - 3
x = 3y
