X = 4 is a vertical line so it's lope is undefined. A line that is perpendicular to a vertical line would be a horizontal line. All horizontal lines have the equation y = # where # is the y-value of the point that the line passes through. For our ordered pair (0.3, 5) the y-value is 5, so the line perpendicular to x = 4 through the point (0.3, 5) would be y = 5