To find the rate of change find the difference in the Y values for every X value.
From X 1 to X 3 the Y value changes by -10
-10 / 2 = -5.
The rate of change is -5.
The initial value is when X = 0
When X is 1, the Y value is 20, using the rate of change of -5, this means when X is 0, the Y value would be 25.
The answer would be, the initial value is 25, rate of change is -5