Answer: -2/3
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Apply the slope formula
m = (y2-y1)/(x2-x1)
m = (8-6)/(2-5)
m = (2)/(-3)
m = -2/3
As you can see, we subtract the y coordinates together. We also subtract the x values together in the same order. If the order is mixed up, then you'll get the wrong sign for the final answer.
The slope is equal to rise over run. Think of "rise" as "change in y", which explains the difference in y values. The run is equal to the change in x, which is the difference in x values.