A line that is parallel to the x-axis is a horizontal line. The general equation of a horizontal line can be expressed in the format \( y = c \), where \( c \) is a constant representing the y-coordinate of all points on the line.
Given the point (-1, 9), the y-coordinate is 9. Therefore, the equation of the line that is parallel to the x-axis and passes through the point (-1, 9) is:
\[ y = 9 \]
This means that for any value of \( x \), the value of \( y \) will always be 9.