(0,2) and (2,-2)
The first number is the x axis, so it goes 2 units from 0 to 2.
The second number is the y axis, so to goes -4 units from 2 to -4
Slope is the rate of change per one unit. (on the x axis)
2has to be divided by 2 to get one unit so -4 has to be divided by 2 as well.
-4/2=-2
That is your solution