Your answer is B) -1/2
One way of finding this answer is by using the slope equation (y2 - y1)/(x2 - x1) and substituting in the coordinates on the line. This gets you
(2 - 3)/(4 - 2) = -1/2
Another way is to find the slope by looking at the graph, and seeing that it must be negative because it slopes downwards to the right instead of up, and that it must be 1/2 because for every 1 unit you go down, you go 2 across, which means your y/x is 1/2.
I hope this helps! Let me know if you have any questions :)