What is the slope (rate of change) of the line?

coordinate plane with linear equation y equals negative 3

The slope (rate of change) of the line represented by the equation y = -3 is 0. Since the equation is y = -3, this means that the y-coordinate of any point on the line will always be -3. Therefore, no matter what change you make in the x-coordinate, the y-coordinate remains constant at -3. This indicates that the line is horizontal and has a slope of 0.