How to find the non-learn function and populate a table, given that I have three known data points, i.e. I have three known (X,Y)

[GusAlmeida]

I have the following table and I need to populate the cells in blank. What is the formula or other function I can use to do that? Bear in mind I want the decrease in churn rate to be the same for each unit variation on the rate.

Rate	Churn Rate
0​	100%​
1​	​
2​	​
3​	​
4​	​
5​	​
6​	​
7​	​
8​	​
9​	​
10​	​
11​	​
12​	​
13​	​
14​	​
15​	​
16​	​
17​	​
18​	​
19​	5%​
20​	​
21​
22​
23​
24​
25​	0%​