The equation of a line parallel to the x-axis is given by a constant value of y. This means that for all values of x, y remains the same.
From the options provided,
- Option #1: \( y = 3x \) is a line with a slope and is not parallel to the x-axis.
- Option #2: \( y = 3 \) is a horizontal line where y is constantly 3, which is parallel to the x-axis.
- Option #3: \( x = 3y \) represents a function where x changes with y; it is not parallel to the x-axis.
- Option #4: \( x = 3 \) is a vertical line, not parallel to the x-axis.
Therefore, the correct answer is Option #2: \( y = 3 \).