What is the rate of change and initial value for the linear relation that includes the points shown in the table?

x y
1 20
3 10
5 0
7 -10
a. initial value: 20, rate of change: 10
b. initial value: 30, rate of change: 10
c. initial value: 25, rate of change: -5
d. initial value: 20, rate of change: -10