Something is wrong here, the slope is off...
m=(y2-y1)/(x2-x1)
m=(1-3)/(12--4)
m=-2/16
m=-1/8
So the point slope form should be:
y-1=(-1/8)(x-12)
The standard form of the line is ax+by=c so we need to rearrange it to reflect the this form...multiply both sides by -8 to get:
8-8y=x-12 subtract 8 from both sides
-8y=x-20 subtract x from both sides
-x-8y=-20 by convention, the coefficient of x should be positive, multiply both sides by -1
x+8y=20
....
Just to show that the equation given you is incorrect..
y-1=(x-12)/4 using the point (-4,3)
3-1=(-4-12)/4
2=-16/4
2=-4 which is obviously incorrect...(they had the wrong slope for the two points given)