Answer:
The equation of the perpendicular line is y=-3x-15.
Step-by-step explanation:
Given the line y=1/3x+6
Comparing it with the slope-intercept form: y=mx+b

Let the slope of the perpendicular line = m
Two lines are perpendicular if the product of their slopes is -1.
Therefore:

To find the equation of the perpendicular line passing through (-9, 12), we use the point-slope form.

Substituting the slope and point (-9,12), we have:

The equation of the perpendicular line is y=-3x-15.