Slope = change in y ÷ change in x = (4 − 5) ÷ (2 − -1) = -1 ÷ 3 = -1/3. Here, slope tells how much y changes for each 1-unit change in x. A negative slope means the line goes downward from left to right, while a positive slope means it goes upward. Always subtract the coordinates in the same order for y and x so the sign of the slope stays correct. The correct answer is -1/3, which matches the calculation or reasoning shown.