I think the answer is y=-3/1x+8
Explanation:
You turn it into y-intercept form because standard form is really hard to understand
x-3y=9
-3y=-x+9
3y=x-9
y=1/3-9
So now we see the slope is 1/3
And we know a perpendicular slope to that would be -3/1
Now if you just add 8 it crosses over point (3,-1)
Brainliest if this helps you?