Answer:
m = -1/3
Explanation:
You have the right idea with the rise and run. We have a run of 15 and a rise (or I guess in this case, a decline) of -5. Slope is rise over run:
-5/15 = -1/3
This means we have a slope of -1/3.
Alternatively, we could just the points and put them into the slope formula.
We have the points (0,25) and (15,20). We can substitute those values into the formula:
m = y₁ - y₂ / x₁ - x₂
m = 25 - 20 / 0 - 15
m = 5/-15
m = -1/3
Works all the same.