Final answer:
The slope of the equation y = -3x is -3, which means the line slopes downwards with a decline of 3 on the y-axis for every 1 unit increase on the x-axis.
Step-by-step explanation:
The question asks about the slope of a line in the context of an equation of a straight line of the form y = mx + b. The slope of a line, represented by the letter 'm', is the rate at which the line rises (or falls) as you move along the line horizontally. In the given equation y = -3x, the slope is the coefficient of the x term, which is -3. Hence, the slope of the line is -3, indicating that for every increase of 1 in the x-value (run), the y-value decreases by 3, leading to a downward sloping line when graphed.