Answer:
-3/4
Explanation:
The rate of change is the change from each perfect point to another.
Here, the points are (0,3) and (4,0).
To get from (0,3) to (4,0), you must go down 3 units and over to the right 4 units. This is the unit of change or -3/4 in this case.
Hope this helps you understand this better. If it doesn't, please let me know through the comment area and I will try to give better examples/help. :)