The slope is rise/run
From the point (6, 4), you must go down 2 units to get to point (6, 2).
Then from point (6, 2), you must go 3 units to the right to get to point (9, 2).
You had to go down 2 and then 3 to the right.
Rise: -2
Run: 3
The slope is -2/3