Final answer:
The equation of a vertical line that passes through the point with an x-coordinate of 3 is x = 3.
Step-by-step explanation:
The equation of a vertical line that passes through a given point on the x-axis is not in the form of y = mx + b, which is the slope-intercept form for non-vertical lines. The equation of a vertical line can only be expressed as x = a, where a is the x-coordinate of the point through which the line passes. Since the vertical line in question goes through the point with an x-coordinate of 3, the equation of this vertical line is simply x = 3.