Explanation:
write equation in terms of x
y=(-6+3x)/12
from this equation u can see your gradient is 3/12 or 1/4
your perpendicular gradient is -1/m (m being the gradient of your main line)
so gradient of perpendicular= -4
since coordinate of main line is given, that point will also be on perpendicular.
so u have point and gradient so u can Calculate line equation
Y=MX+C
(-7)=(-4)(-1)+c
c=-11
y=-4x-11
^equation of perpendicular