Answer:
-1/3
Explanation:
First step to determine what's the slope of a perpendicular is to know the slope of the line we're referring to.
What's the slope of 3x + y = 4?
The slope is given by the factor of the variable x... so in this case the slope is 3, which is a positive slope, the line is going up.
To have another line crossing that one with a 90 degrees angle, it would have to be with a negative slope.
The slope angle would also to be inverted... so from 3 would go to 1/3.
In a shortcut, to find a perpendicular slope to m (the original slope), you do -1/m.
So the slope of the perpendicular would be -1/3.