Since the first line passes thru the origin, you can read off its slope from the coordinates of the other point (3,2): the slope is m = 2/3.
A line perpendicular to the first has slope -3/2, the negative reciprocal of 2/3.
Thus, the perpendicular line is y = (-3/2)x + b. Subbing 0 for y and 0 for x, we get b = 0. Therefore, the equation of this new line is y = (-3/2)x.
