Final answer:
The equation of a line passing through (4,5) and parallel to the y-axis is x = 4.
Step-by-step explanation:
To find the equation of a line parallel to the y-axis and passing through a given point, we need to consider that a line parallel to the y-axis has the equation x = c, where c is the x-coordinate of any point on the line. In this case, since the line passes through (4,5), the equation of the line is x = 4. This is because no matter what value of y we plug into the equation, the x-coordinate will always be 4.