Question 211350
3x-y=9 
-y=-3x+9
y=3x+9 ( red line)this line has a slope of 3.
Therefore all perpendicular lines will have a slope=-1/3
kx+3y=5
3y=-kx+5
y=-kx/3+5/3 
[-k/3=-1/3]
k=1 ans.
y=-x/3+5/3 (green line)
{{{ graph( 200, 200, -10, 10, -10, 10, 3x +9, -x/3 +5/3) }}} (graph 200x200 pixels, x from -10 to 10, y from -10 to 10, of TWO functions 3x +9 and -x/3 +5/3).