I would start this problem by setting up a table.
In the left column, we will have our x values
and in the right column, we have our y values.
Put our first ordered pair on the top and second on bottom.
We can see the y values go from 6 to 9 so change in y is 3.
The x values go from 0 to -3 so change in x is -3.
The slope is equal to the rate of change or change in y / change in x.
So our slope is 3/-3 of -1.
