If the equation of a line is y = mx + c, where m is the slope, then the slope of the line perpendicular to this line is -1/m.
We have x - 4y = -12, let’s make it in the form y = mx + c
4y = x+12
y = (1/4)x + 3
The slope of this line is (1/4)
Slope of perpendicular line will be -4