Answer:
Slope: -2
Explanation:
(This answer is if you meant to write 6y = 3x - 9)
First, change the standard equation form into a linear equation form, y=mx+b. To do this, divide both sides by 6 to get:

This can then simplify to:

In order to find the equation of a perpendicular line, you need to find the opposite reciprocal of the current slope:

The slope is m, meaning that the slope of the perpendicular equation is -2.
Hope this helps!