Since we don't see what you are dealing with, I'll do my best to explain.
The rate of change, also lnown as the slope, is basically the unit rate, change in y/change in x.
If y = 6 when x = 0 and y = 4 when x = 2, then your rate of change is (6 - 4)/(0 - 2) = 2/-2 = -1.
Note, you have to go the same direction. You can also say (4 - 6)/(2 - 0) = -2/2 = -1 but NOT (6 - 4)/(2 - 0) = 2/2 = 1 or (4 - 6)/(0 - 2) = -2/-2 = 1.
Hope this helps!
