What are the points on the y-axis whose distance from the line 
is 4 units.
The given line can be written as 4x + 3y -12 = 0
On comparing equation (1) to the general equation of line Ax + By + C = 0, we get,
A = 4 , B = 3 and C = -12.
It is known that the perpendicular distance (d) of the line Ax + By + C = 0 from a point
(x1, y1) is given by
Therefore, if (0,b) is the point on the y – axis whose distance from line 
is 4 units, then,
=> 20 = |3b – 12|
=> 20 = 
(3b – 12)
=> 20 = (3b – 12) or 20 = -(3b-12)
=> 3b = 20 +12 or 3b = -20 +12
=> 
Therefore, the required points are 
4