The equation of a line parallel to x-axis and at a distance of 5 units below it, is:

1. x – 5 = 0

2. x + 5 = 0

3. y – 5 = 0

4. y + 5 = 0

Any line parallel to the x-axis is a horizontal line and has the equation of form y = k.

The distance is 5 units below x-axis, thus the y-coordinate (k) of every point on the line is -5.

y = -5

y + 5 = 0.

Hence, option 4 is the correct option.